- Ghost
- Ghoul hand 102.3
- Gianotti Crosti syndrome 057.8
- Giant
- Giardia lamblia infestation 007.1
- Giardiasis 007.1
- Gibert's disease (pityriasis rosea) 696.3
- Gibraltar fever - see Brucellosis
- Giddiness 780.4
- Gierke's disease (glycogenosis I) 271.0
- Gigantism (cerebral) (hypophyseal) (pituitary) 253.0
- Gilbert's disease or cholemia (familial nonhemolytic jaundice) 277.4
- Gilchrist's disease (North American blastomycosis) 116.0
- Gilford (-Hutchinson) disease or syndrome (progeria) 259.8
- Gilles de la Tourette's disease (motor-verbal tic) 307.23
- Gillespie's syndrome (dysplasia oculodentodigitalis) 759.89
- Gingivitis 523.10
- Gingivoglossitis 529.0
- Gingivopericementitis 523.40
- Gingivosis 523.10
- Gingivostomatitis 523.10
- Giovannini's disease 117.9