See Rare Diseases by First Letter (T)
- T-Lymphocytopenia
- Takayasu Arteritis
- Talipes Equinovarus
- Tangier Disease
- Tay Sachs Disease
- Testicular Cancer
- Testotoxicosis
- Tetanus
- Tetrahydrobiopterin Deficiency
- Tetralogy of Fallot
- Thalassemia
- Thoracic Outlet Syndrome
- Thrombasthenia
- Thrombotic Thrombocytopenic Purpura, Acquired
- Thrombotic Thrombocytopenic Purpura, Congenital
- Thymic Epithelial Tumor
- Thyroid Cancer, Anaplastic
- Thyroid Cancer, Follicular
- Thyroid Cancer, Medullary
- Thyrotoxic Periodic Paralysis
- Tick-borne Encephalitis
- Tongue Cancer
- Toni-Debre-Fanconi Syndrome
- Toxic Epidermal Necrolysis
- Toxocariasis
- Tracheobronchomalacia
- Tracheoesophageal Fistula
- Trachoma
- Transitional Cell Carcinoma
- Transposition of the Great Arteries
- Transverse Myelitis
- Tremor Hereditary Essential, 1
- Treponema Infection
- Trichotillomania
- Trichuriasis
- Tricuspid Atresia
- Trigeminal Neuralgia
- Trigger Thumb
- Trisomy 13
- Trisomy 18
- Tropical Sprue
- Trypanosomiasis, Human East-African
- Tuberculosis
- Tuberculous Meningitis
- Tuberous Sclerosis
- Tubular Aggregate Myopathy
- Tufted Angioma
- Tufting Enteropathy
- Tularemia
- Turner Syndrome
- Twin Twin Transfusion Syndrome
- Tylosis
- Typhoid Fever
- Typhus
- Tyrosinemia Type 1