- Teratoma (solid) (M9080/1) - see also Neoplasm, by site, uncertain behavior
- Terminal care V66.7
- Termination
- Ternidens diminutus infestation 127.7
- Terrors, night (child) 307.46
- Terry's syndrome (see also Retinopathy of prematurity) 362.21
- Tertiary - see condition
- Tessellated fundus, retina (tigroid) 362.89
- Test(s)
- Testicle, testicular, testis - see also condition
- Tetanus, tetanic (cephalic) (convulsions) 037
- Tetany, tetanic 781.7
- Tetralogy of Fallot 745.2
- Tetraplegia - see Quadriplegia
- Thailand hemorrhagic fever 065.4
- Thalassanemia 282.40
- Thalassemia (disease) 282.40
- Thalassemic variants 282.49
- Thaysen-Gee disease (nontropical sprue) 579.0
- Thecoma (M8600/0) 220
- Thelarche, precocious 259.1
- Thelitis 611.0
