OB
- Obstructive sleep apnea, pediatric (See: Pediatric obstructive sleep apnea)
OC
- Ocular melanoma (See: Eye melanoma)
OR
- Oral cancer (See: Lip cancer)
- Oral candidiasis (See: Oral thrush)
OS
- Osteitis deformans (See: Paget’s disease of bone)
- Osteonecrosis (See: Avascular necrosis (osteonecrosis))
- Osteophytes (See: Bone spurs)
OT
- Otitis externa (See: Swimmer's ear)
