- Tumefaction - see also Swelling
- Tumor (M8000/1) - see also Neoplasm, by site, unspecified nature
- Tumorlet (M8040/1) - see Neoplasm, by site, uncertain behavior
- Tungiasis 134.1
- Tunica vasculosa lentis 743.39
- Tunnel vision 368.45
- Turban tumor (M8200/0) 216.4
- Türck's trachoma (chronic catarrhal laryngitis) 476.0
- Türk's syndrome (ocular retraction syndrome) 378.71
- Turner's
- Turner-Kieser syndrome (hereditary osteo-onychodysplasia) 756.89
- Turner-Varny syndrome 758.6
- Turricephaly 756.0
- Tussis convulsiva (see also Whooping cough) 033.9
- Twiddler's syndrome (due to)
- Twin
- Twinning, teeth 520.2
- Twist, twisted
- Twitch 781.0
- Tylosis 700
- Tympanism 787.3
- Tympanites (abdominal) (intestine) 787.3