Obesity
Obesity Hypoventilation Syndrome
Obesophobia (Fear of Gaining Weight)
Oblique Fracture
Obsessive-Compulsive Disorder (OCD)
Obsessive-Compulsive Personality Disorder (OCPD)
Obstructed Defecation
Obstructive Shock
Obstructive Sleep Apnea
Occipital Neuralgia
Octophobia (Fear of the Number 8)
Ocular Herpes (Eye Herpes)
Ocular Hypertension
Ocular Ischemic Syndrome
Ocular Migraine
Ocular Rosacea
Ocular Syphilis
Oculopharyngeal Muscular Dystrophy
Ogilvie Syndrome
Oligoarthritis
Oligodendroglioma
Oligohydramnios
Oligomenorrhea
Oligospermia (Low Sperm Count)
Oliguria (Low Urine Output)
Ombrophobia (Fear of Rain)
Omega-3 Fatty Acids
Omentum Cancer
Omphalitis
Omphalocele
Onchocerciasis (River Blindness)
Oncogenes
Onycholysis
Open Globe Injury
Ophidiophobia (Fear of Snakes
Opioid Overdose
Opioid Use Disorder
Opisthotonos
Oppositional Defiant Disorder (ODD)
Optic Atrophy
Optic Disc Drusen
Optic Nerve Hypoplasia (Includes Septo-Optic Dysplasia)
Optic Neuritis
Oral Allergy Syndrome
Oral Cancer
Oral Lichen Planus
Oral Mucocele
Orbital Cellulitis
Orbital Fractures
Orbital Hypertelorism
Orchitis
Organ Failure
Ornithophobia (Fear of Birds)
Orofacial Granulomatosis
Oropharyngeal Cancer
Oropharyngeal Human Papillomavirus (HPV) Infection
Orthopnea
Orthopoxvirus
Orthostatic Hypotension
Orthostatic Proteinuria
Os Trigonum Syndrome
Osgood-Schlatter Disease
Ossifying Fibroma
Osteitis Pubis
Osteoarthritis
Osteoarthritis of the Knee
Osteoblastoma
Osteochondritis Dissecans (OCD)
Osteochondroma
Osteogenesis Imperfecta (OI)
Osteoid Osteoma
Osteomalacia
Osteomyelitis (Bone Infection)
Osteonecrosis of the Jaw (ONJ)
Osteopenia
Osteopoikilosis
Osteoporosis
Osteoradionecrosis (ORN)
Osteosarcoma
Otosclerosis
Ototoxicity
Ovarian Cancer
Ovarian Cysts
Ovarian Dermoid Cyst
Ovarian Endometrioma
Ovarian Germ Cell Tumors
Ovarian Hyperstimulation Syndrome (OHSS)
Ovary Pain
Overactive Bladder
Overbite
Overeating
Overflow Incontinence
Overpronation
Overriding Aorta
Overtraining Syndrome
Ovulation Pain
Oxidative Stress