This is a list of diseases starting with the letter "O".
- O Doherty syndrome
- O Donnell Pappas syndrome
- Obesophobia
- Obsessive–compulsive disorder (OCD)
- Obsessive–compulsive personality disorder
- Obstructive asymmetric septal hypertrophy
- Obstructive sleep apnea
- Occipital horn syndrome
- Occlusive infantile arteriopathy
- Occult spinal dysraphism
- Occupational asthma
- Occupational asthma - animals, insects and fungi
- Occupational asthma - chemicals and materials
- Occupational asthma - drugs and enzymes
- Occupational asthma - grains, flours, plants and gums
- Occupational asthma - isocyanates and metals
- Occupational asthma - wood
- OCD
- Ochoa syndrome
- Ochronosis, hereditary
- Ochronosis
- Ockelbo disease
- Ocular albinism
- Ocular coloboma-imperforate anus
- Ocular convergence spasm
- Ocular histoplasmosis
- Ocular melanoma
- Ocular motility disorders
- Ocular toxoplasmosis
- Oculo-auriculo-vertebral spectrum
- Oculo cerebral dysplasia
- Oculo cerebro acral syndrome
- Oculo cerebro osseous syndrome
- Oculo dento digital dysplasia
- Oculo digital syndrome
- Oculo facio cardio dental syndrome
- Oculo skeletal renal syndrome
- Oculo tricho anal syndrome
- Oculo tricho dysplasia
- Oculoauriculofrontonasal syndrome
- Oculo-auriculo-vertebral dysplasia
- Oculocerebral hypopigmentation syndrome Cross type
- Oculocerebral hypopigmentation syndrome type Preus
- Oculocerebral syndrome with hypopigmentation
- Oculocerebrocutaneous syndrome
- Oculocerebrorenal syndrome
- Oculocutaneous albinism immunodeficiency
- Oculocutaneous albinism type 1
- Oculocutaneous albinism type 2
- Oculocutaneous albinism type 3
- Oculocutaneous albinism, tyrosinase negative
- Oculocutaneous albinism, tyrosinase positive
- Oculocutaneous tyrosinemia
- Oculodental syndrome Rutherfurd syndrome
- Oculodentodigital dysplasia dominant
- Oculodentodigital syndrome
- Oculo-dento-digital syndrome
- Oculodentoosseous dysplasia dominant
- Oculodentoosseous dysplasia recessive
- Oculodigitoesophagoduodenal syndrome
- Oculo-gastrointestinal muscular dystrophy
- Oculomaxillofacial dysostosis
- Oculomaxillofacial dysplasia with oblique facial clefts
- Oculomelic amyoplasia
- Oculomotor nerve palsy
- Oculopalatoskeletal syndrome
- Oculopharyngeal muscular dystrophy
- Oculorenocerebellar syndrome
- Odonto onycho dysplasia with alopecia
- Odontoma
- Odontomicronychial dysplasia
- Odontoonychodermal dysplasia
- Odontophobia
- Odontotrichomelic hypohidrotic dysplasia
- OFD syndrome type 8
- OFD syndrome type Figuera
- Ogilvie's syndrome
- Ohaha syndrome
- Ohdo–Madokoro–Sonoda syndrome
- Oikophobia
- Okamuto–Satomura syndrome
- Olfactophobia
- Oligodactyly
- Oligodactyly tetramelia postaxial
- Oligomeganephronic renal hypoplasia
- Oligomeganephrony
- Oligophernia
- Oliver–McFarlane syndrome
- Oliver syndrome
- Olivopontocerebellar atrophy deafness
- Olivopontocerebellar atrophy type 1
- Olivopontocerebellar atrophy type 2
- Olivopontocerebellar atrophy type 3
- Olivopontocerebellar atrophy
- Ollier disease
- Olmsted syndrome
- Olney's lesions
- Omenn syndrome
- Omodysplasia type 1
- Omodysplasia type 2
- Omphalocele cleft palate syndrome lethal
- Omphalocele exstrophy imperforate anus
- Omphalomesenteric cyst
- Omsk hemorrhagic fever
- Onat syndrome
- Onchocerciasis
- Oncocytoma
- Ondine's curse
- Oneirophobia
- Onychocryptosis
- Onychogryphosis
- Onycholysis
- Onychomadesis
- Onychomatricoma
- Onychomycosis
- Onychonychia hypoplastic distal phalanges
- Onychophosis
- Onychotrichodysplasia and neutropenia
- Opioid dependence
- Opioid-induced hyperalgesia
- Ophthalmic icthyosis
- Ophthalmo acromelic syndrome
- Ophthalmomandibulomelic dysplasia
- Ophthalmophobia
- Ophthalmoplegia ataxia hypoacusis
- Ophthalmoplegia mental retardation lingua scrotalis
- Ophthalmoplegia myalgia tubular aggregates
- Ophthalmoplegia progressive external scoliosis
- Opitz–Mollica–Sorge syndrome
- Opitz–Reynolds–Fitzgerald syndrome
- Opitz syndrome
- Opportunistic infections
- Oppositional defiant disorder
- Opsismodysplasia
- Optic atrophy ophthalmoplegia ptosis deafness myopia
- Optic atrophy polyneuropathy deafness
- Optic atrophy, autosomal dominant
- Optic atrophy, idiopathic, autosomal recessive
- Optic atrophy
- Optic disc drusen
- Optic nerve coloboma with renal disease
- Optic nerve disorder
- Optic nerve hypoplasia, familial bilateral
- Optic neuritis
- Optic pathway glioma
- Opticoacoustic nerve atrophy dementia
- Oral facial digital syndrome type 3
- Oral facial digital syndrome type 4
- Oral facial digital syndrome
- Oral facial dyskinesia
- Oral leukoplakia
- Oral lichen planus
- Oral lichenoid lesions
- Oral squamous cell carcinoma
- Oral submucous fibrosis
- Oral-facial cleft
- Oral-facial-digital syndrome, type IV
- Oral-facial-digital syndrome
- Oral-pharyngeal disorders
- Organic brain syndrome
- Organic mood syndrome
- Organic personality syndrome
- Organophosphate poisoning
- Ornithine aminotransferase deficiency
- Ornithine carbamoyl phosphate deficiency
- Ornithine transcarbamylase deficiency, hyperammonemia due to
- Ornithinemia
- Ornithosis
- Oro acral syndrome
- Orofaciodigital syndrome Gabrielli type
- Orofaciodigital syndrome Shashi type
- Orofaciodigital syndrome Thurston type
- Orofaciodigital syndrome type 2
- Orofaciodigital syndrome type1
- Orotic aciduria hereditary
- Orotic aciduria purines-pyrimidines
- Orotidylic decarboxylase deficiency
- Orstavik Lindemann Solberg syndrome
- Orthostatic intolerance
- Osebold–Remondini syndrome
- Osgood–Schlatter disease
- OSLAM syndrome
- Osmed syndrome
- Ossicular malformations, familial
- Osteoarthritis
- Osteoarthropathy of fingers familial
- Osteochondritis deformans juvenile
- Osteochondritis dissecans
- Osteochondritis
- Osteochondrodysplasia thrombocytopenia hydrocephalus
- Osteochondroma
- Osteocraniostenosis
- Osteodysplasia familial Anderson type
- Osteodysplastic dwarfism Corsello type
- Osteoectasia familial
- Osteogenesis Imperfecta
- Osteogenesis imperfecta congenita microcephaly and cataracts
- Osteogenesis imperfecta congenital joint contractures
- Osteogenesis imperfecta retinopathy
- Osteogenic sarcoma
- Osteoglophonic dwarfism
- Osteolysis hereditary multicentric
- Osteolysis syndrome recessive
- Osteomalacia
- Osteomyelitis
osteocytes
- Osteonecrosis
- Osteopathia condensans disseminata with osteopoikilosis
- Osteopathia striata cranial sclerosis
- Osteopathia striata pigmentary dermopathy white forelock
- Osteopetrosis autosomal dominant type 1
- Osteopetrosis lethal
- Osteopetrosis renal tubular acidosis
- Osteopetrosis, (generic term)
- Osteopetrosis, malignant
- Osteopetrosis, mild autosomal recessive form
- Osteopoikilosis
- Osteoporosis macrocephaly mental retardation blindness
- Osteoporosis oculocutaneous hypopigmentation syndrome
- Osteoporosis pseudoglioma syndrome
- Osteoporosis
- Osteosarcoma limb anomalies erythroid macrocytosis
- Osteosclerose type Stanescu
- Osteosclerosis abnormalities of nervous system and meninges
- Osteosclerosis autosomal dominant Worth type
- Osteosclerosis
- Osteocytes
- Ota–Appaura syndrome
- Ota–Kawamura–Ito syndrome
- Oto-palato-digital syndrome type I and II
- Otodental syndrome
- Otofaciocervical syndrome
- Otoonychoperoneal syndrome
- Oto-Palatal-digital syndrome
- Otopalatodigital syndrome type 2
- Otosclerosis, familial
- Otosclerosis
- Otospondylomegaepiphyseal dysplasia
- Ouvrier–Billson syndrome
- Ovarian cancer
- Ovarian carcinosarcoma
- Ovarian dwarfism as part of Turner syndrome
- Ovarian dwarfism
- Ovarian insufficiency due to FSH resistance
- ovarian remnant syndrome
- Overfolded helix
- Overgrowth radial ray defect arthrogryposis
- Overgrowth syndrome type Fryer
- Overhydrated hereditary stomatocytosis
- Overwhelming post-splenectomy infection (OPSI)
- Oxalosis
This is a list of diseases starting with the letter "O".
- O Doherty syndrome
- O Donnell Pappas syndrome
- Obesophobia
- Obsessive–compulsive disorder (OCD)
- Obsessive–compulsive personality disorder
- Obstructive asymmetric septal hypertrophy
- Obstructive sleep apnea
- Occipital horn syndrome
- Occlusive infantile arteriopathy
- Occult spinal dysraphism
- Occupational asthma
- Occupational asthma - animals, insects and fungi
- Occupational asthma - chemicals and materials
- Occupational asthma - drugs and enzymes
- Occupational asthma - grains, flours, plants and gums
- Occupational asthma - isocyanates and metals
- Occupational asthma - wood
- OCD
- Ochoa syndrome
- Ochronosis, hereditary
- Ochronosis
- Ockelbo disease
- Ocular albinism
- Ocular coloboma-imperforate anus
- Ocular convergence spasm
- Ocular histoplasmosis
- Ocular melanoma
- Ocular motility disorders
- Ocular toxoplasmosis
- Oculo-auriculo-vertebral spectrum
- Oculo cerebral dysplasia
- Oculo cerebro acral syndrome
- Oculo cerebro osseous syndrome
- Oculo dento digital dysplasia
- Oculo digital syndrome
- Oculo facio cardio dental syndrome
- Oculo skeletal renal syndrome
- Oculo tricho anal syndrome
- Oculo tricho dysplasia
- Oculoauriculofrontonasal syndrome
- Oculo-auriculo-vertebral dysplasia
- Oculocerebral hypopigmentation syndrome Cross type
- Oculocerebral hypopigmentation syndrome type Preus
- Oculocerebral syndrome with hypopigmentation
- Oculocerebrocutaneous syndrome
- Oculocerebrorenal syndrome
- Oculocutaneous albinism immunodeficiency
- Oculocutaneous albinism type 1
- Oculocutaneous albinism type 2
- Oculocutaneous albinism type 3
- Oculocutaneous albinism, tyrosinase negative
- Oculocutaneous albinism, tyrosinase positive
- Oculocutaneous tyrosinemia
- Oculodental syndrome Rutherfurd syndrome
- Oculodentodigital dysplasia dominant
- Oculodentodigital syndrome
- Oculo-dento-digital syndrome
- Oculodentoosseous dysplasia dominant
- Oculodentoosseous dysplasia recessive
- Oculodigitoesophagoduodenal syndrome
- Oculo-gastrointestinal muscular dystrophy
- Oculomaxillofacial dysostosis
- Oculomaxillofacial dysplasia with oblique facial clefts
- Oculomelic amyoplasia
- Oculomotor nerve palsy
- Oculopalatoskeletal syndrome
- Oculopharyngeal muscular dystrophy
- Oculorenocerebellar syndrome
- Odonto onycho dysplasia with alopecia
- Odontoma
- Odontomicronychial dysplasia
- Odontoonychodermal dysplasia
- Odontophobia
- Odontotrichomelic hypohidrotic dysplasia
- OFD syndrome type 8
- OFD syndrome type Figuera
- Ogilvie's syndrome
- Ohaha syndrome
- Ohdo–Madokoro–Sonoda syndrome
- Oikophobia
- Okamuto–Satomura syndrome
- Olfactophobia
- Oligodactyly
- Oligodactyly tetramelia postaxial
- Oligomeganephronic renal hypoplasia
- Oligomeganephrony
- Oligophernia
- Oliver–McFarlane syndrome
- Oliver syndrome
- Olivopontocerebellar atrophy deafness
- Olivopontocerebellar atrophy type 1
- Olivopontocerebellar atrophy type 2
- Olivopontocerebellar atrophy type 3
- Olivopontocerebellar atrophy
- Ollier disease
- Olmsted syndrome
- Olney's lesions
- Omenn syndrome
- Omodysplasia type 1
- Omodysplasia type 2
- Omphalocele cleft palate syndrome lethal
- Omphalocele exstrophy imperforate anus
- Omphalomesenteric cyst
- Omsk hemorrhagic fever
- Onat syndrome
- Onchocerciasis
- Oncocytoma
- Ondine's curse
- Oneirophobia
- Onychocryptosis
- Onychogryphosis
- Onycholysis
- Onychomadesis
- Onychomatricoma
- Onychomycosis
- Onychonychia hypoplastic distal phalanges
- Onychophosis
- Onychotrichodysplasia and neutropenia
- Opioid dependence
- Opioid-induced hyperalgesia
- Ophthalmic icthyosis
- Ophthalmo acromelic syndrome
- Ophthalmomandibulomelic dysplasia
- Ophthalmophobia
- Ophthalmoplegia ataxia hypoacusis
- Ophthalmoplegia mental retardation lingua scrotalis
- Ophthalmoplegia myalgia tubular aggregates
- Ophthalmoplegia progressive external scoliosis
- Opitz–Mollica–Sorge syndrome
- Opitz–Reynolds–Fitzgerald syndrome
- Opitz syndrome
- Opportunistic infections
- Oppositional defiant disorder
- Opsismodysplasia
- Optic atrophy ophthalmoplegia ptosis deafness myopia
- Optic atrophy polyneuropathy deafness
- Optic atrophy, autosomal dominant
- Optic atrophy, idiopathic, autosomal recessive
- Optic atrophy
- Optic disc drusen
- Optic nerve coloboma with renal disease
- Optic nerve disorder
- Optic nerve hypoplasia, familial bilateral
- Optic neuritis
- Optic pathway glioma
- Opticoacoustic nerve atrophy dementia
- Oral facial digital syndrome type 3
- Oral facial digital syndrome type 4
- Oral facial digital syndrome
- Oral facial dyskinesia
- Oral leukoplakia
- Oral lichen planus
- Oral lichenoid lesions
- Oral squamous cell carcinoma
- Oral submucous fibrosis
- Oral-facial cleft
- Oral-facial-digital syndrome, type IV
- Oral-facial-digital syndrome
- Oral-pharyngeal disorders
- Organic brain syndrome
- Organic mood syndrome
- Organic personality syndrome
- Organophosphate poisoning
- Ornithine aminotransferase deficiency
- Ornithine carbamoyl phosphate deficiency
- Ornithine transcarbamylase deficiency, hyperammonemia due to
- Ornithinemia
- Ornithosis
- Oro acral syndrome
- Orofaciodigital syndrome Gabrielli type
- Orofaciodigital syndrome Shashi type
- Orofaciodigital syndrome Thurston type
- Orofaciodigital syndrome type 2
- Orofaciodigital syndrome type1
- Orotic aciduria hereditary
- Orotic aciduria purines-pyrimidines
- Orotidylic decarboxylase deficiency
- Orstavik Lindemann Solberg syndrome
- Orthostatic intolerance
- Osebold–Remondini syndrome
- Osgood–Schlatter disease
- OSLAM syndrome
- Osmed syndrome
- Ossicular malformations, familial
- Osteoarthritis
- Osteoarthropathy of fingers familial
- Osteochondritis deformans juvenile
- Osteochondritis dissecans
- Osteochondritis
- Osteochondrodysplasia thrombocytopenia hydrocephalus
- Osteochondroma
- Osteocraniostenosis
- Osteodysplasia familial Anderson type
- Osteodysplastic dwarfism Corsello type
- Osteoectasia familial
- Osteogenesis Imperfecta
- Osteogenesis imperfecta congenita microcephaly and cataracts
- Osteogenesis imperfecta congenital joint contractures
- Osteogenesis imperfecta retinopathy
- Osteogenic sarcoma
- Osteoglophonic dwarfism
- Osteolysis hereditary multicentric
- Osteolysis syndrome recessive
- Osteomalacia
- Osteomyelitis
osteocytes
- Osteonecrosis
- Osteopathia condensans disseminata with osteopoikilosis
- Osteopathia striata cranial sclerosis
- Osteopathia striata pigmentary dermopathy white forelock
- Osteopetrosis autosomal dominant type 1
- Osteopetrosis lethal
- Osteopetrosis renal tubular acidosis
- Osteopetrosis, (generic term)
- Osteopetrosis, malignant
- Osteopetrosis, mild autosomal recessive form
- Osteopoikilosis
- Osteoporosis macrocephaly mental retardation blindness
- Osteoporosis oculocutaneous hypopigmentation syndrome
- Osteoporosis pseudoglioma syndrome
- Osteoporosis
- Osteosarcoma limb anomalies erythroid macrocytosis
- Osteosclerose type Stanescu
- Osteosclerosis abnormalities of nervous system and meninges
- Osteosclerosis autosomal dominant Worth type
- Osteosclerosis
- Osteocytes
- Ota–Appaura syndrome
- Ota–Kawamura–Ito syndrome
- Oto-palato-digital syndrome type I and II
- Otodental syndrome
- Otofaciocervical syndrome
- Otoonychoperoneal syndrome
- Oto-Palatal-digital syndrome
- Otopalatodigital syndrome type 2
- Otosclerosis, familial
- Otosclerosis
- Otospondylomegaepiphyseal dysplasia
- Ouvrier–Billson syndrome
- Ovarian cancer
- Ovarian carcinosarcoma
- Ovarian dwarfism as part of Turner syndrome
- Ovarian dwarfism
- Ovarian insufficiency due to FSH resistance
- ovarian remnant syndrome
- Overfolded helix
- Overgrowth radial ray defect arthrogryposis
- Overgrowth syndrome type Fryer
- Overhydrated hereditary stomatocytosis
- Overwhelming post-splenectomy infection (OPSI)
- Oxalosis