- Coccyx - see condition
- Cochin-China
- Cock's peculiar tumor 706.2
- Cockayne's disease or syndrome (microcephaly and dwarfism) 759.89
- Cockayne-Weber syndrome (epidermolysis bullosa) 757.39
- Cocked-up toe 735.2
- Codman's tumor (benign chondroblastoma) (M9230/0) - see Neoplasm, bone, benign
- Coenurosis 123.8
- Coffee workers' lung 495.8
- Cogan's syndrome 370.52
- Coiling, umbilical cord - see Complications, umbilical cord
- Coitus, painful (female) 625.0
- Cold 460
- Coldsore (see also Herpes, simplex) 054.9
- Colibacillosis 041.4
- Colibacilluria 791.9
- Colic (recurrent) 789.7
- Colicystitis (see also Cystitis) 595.9
- Colitis (acute) (catarrhal) (croupous) (cystica superficialis) (exudative) (hemorrhagic) (noninfectious) (phlegmonous) (presumed noninfectious) 558.9
- Collagen disease NEC 710.9
- Collagenosis (see also Collagen disease) 710.9
- Collapse 780.2