- Obesity
- Obsessive compulsive disorder
- Orthodontics
- Osteoarthritis
- Osteomyelitis
- Osteopathy
- Osteoporosis
- Otitis externa
- Otitis media
- Out-of-hours services
- Ovarian cyst
- Oesophageal cancer
- Ovarian cancer
- Oedema
- Oral thrush in adults
- Oral thrush in babies
- Organ donation
- Obstructive sleep apnoea
- Onychomycosis
- Oral cancer
- Overweight
- Oligomenorrhoea
- Over-active thyroid