- Twinning, teeth 520.2
- Twist, twisted
- Twitch 781.0
- Tylosis 700
- Tympanism 787.3
- Tympanites (abdominal) (intestine) 787.3
- Tympanitis - see Myringitis
- Tympanosclerosis 385.00
- Tympanum - see condition
- Tympany
- Typhlitis (see also Appendicitis) 541
- Typhoenteritis 002.0
- Typhogastric fever 002.0
- Typhoid (abortive) (ambulant) (any site) (fever) (hemorrhagic) (infection) (intermittent) (malignant) (rheumatic) 002.0
- Typhomalaria (fever) (see also Malaria) 084.6
- Typhomania 002.0
- Typhoperitonitis 002.0
- Typhus (fever) 081.9
- Tyrosinemia 270.2
- Tyrosinosis (Medes) (Sakai) 270.2
- Tyrosinuria 270.2
- Tyrosyluria 270.2