- Tachycardia (fast heart rate)
- Takayasu's arteritis (Giant cell arteritis of the young)
- Tape worm infection
- Tarantula bite
- Tarsal tunnel syndrome (foot nerve damage)
- Tay-Sachs disease
- Tear duct infection (Dacryocystitis)
- Teething
- Temporal arteritis (inflamed scalp artery)
- Temporal lobe epilepsy (non-convulsive seizure)
- Temporomandibular disorders
- Temporomandibular joint syndrome (TMJ, jaw joint pain)
- Tendon laceration (tendon cut)
- Tendonitis (tendon inflammation)
- Tennis elbow (lateral epicondylitis)
- Tenosynovitis (tendon sheath inflammation)
- Tension headache (stress headache)
- Tension pneumothorax (dangerous lung collapse)
- Testicular cancer (tumor)
- Testicular hypofunction
- Testicular torsion (twisting of testicle)
- Tetanus (lockjaw)
- Thalassemia (Mediterranean anemia, inherited blood disorder)
- Third cranial nerve disorder (disorder of eye movement)
- Thoracic outlet syndrome (nerve, blood vessel compression)
- Thoracic spine stenosis
- Thoracic spondylosis (spine arthritis)
- Thrombocytopenia (low platelet count)
- Thrombophlebitis (superficial)
- Thrombotic stroke
- Thrombotic thrombocytopenia purpura (TTP, rare blood disorder)
- Thrush (oral candidiasis)
- Thyroglossal duct cyst (neck cyst)
- Thyroid cancer (neck gland cancer)
- Thyroiditis (thyroid inflammation)
- Tic Disorder
- Tick bite
- Tick borne encephalitis (brain infection)
- Tick paralysis (toxin from ticks)
- Tinea (fungal skin infection)
- Tinea versicolor
- Tinnitus
- Toe fracture
- Toe laceration (cut skin)
- Toe swelling
- Toenail fungus (Onychomycosis)
- Tongue cancer (tumor)
- Tonsillar cancer (tumor)
- Tonsillitis (tonsil infection)
- Trench foot (immersion foot)
- Tooth abrasion and erosion
- Tooth discoloration
- Tooth infection
- Toothache
- Tooth infection
- Torticollis, spasmodic (neck muscle spasm)
- Tori
- Tourette syndrome (repetitive involuntary movements, vocalizations)
- Toxic shock syndrome (life-threatening bacterial infection complication)
- Toxic megacolon (rapid dilation of the colon)
- Toxoplasma infection (parasite infection)
- Transient global amnesia (sudden period of short-term memory loss)
- Transient ischemic attack (TIA, reversible stroke)
- Transverse myelitis (spinal cord inflammation)
- Trauma
- Traumatic brain injury
- Traumatic hip dislocation
- Traumatic injuries of the lips and tongue
- Traumatic nerve injury
- Traveler's diarrhea (Montezuma's revenge)
- Treponema pallidum (syphilis)
- Triangular fibrocartilage complex injury (wrist injury)
- Trichinella spiralis infection (trichinosis, parasitic infection from undercooked pork)
- Trichomonas vaginalis infection (vaginal infection)
- Trigeminal neuralgia (facial nerve pain)
- Trigger finger
- Triple negative breast cancer
- Trismus
- Tropical sprue
- Tuberculosis infection (TB)
- Tubo ovarian abscess (pelvic abscess)
- Tularemia (bacterial infection)
- Turner syndrome (gonadal dysgenesis)
- Tylenol (acetaminophen) overdose
- Tylenol (acetaminophen) poisoning
- Typhoid fever (salmonella typhi infection from contaminated food or water)