See Rare Diseases by First Letter (H)
- Haemophilus Influenzae
- Hailey-Hailey Disease
- Hairy Cell Leukemia
- Hand-Schuller-Christian Disease
- Hansen's Disease
- Hantavirus Pulmonary Syndrome
- Heart Tumor
- Heavy Metal Poisoning
- HELLP Syndrome
- Helminthiasis
- Hemangioblastoma
- Hemangioendothelioma
- Hemangiopericytoma
- Hemifacial Microsomia
- Hemiplegia
- Hemiplegic Migraine
- Hemoglobin C Disease
- Hemoglobin SC Disease
- Hemolytic Uremic Syndrome
- Hemophagocytic Lymphohistiocytosis
- Hemophilia
- Hemophilia A, Acquired
- Hemophilia A, Congenital
- Hemophilia B
- Hemophilic Arthropathy
- Hemorrhagic Fever
- Hemosiderosis
- Henoch-Schonlein Purpura
- Heparin-induced Thrombocytopenia
- Hepatic Encephalopathy
- Hepatitis E
- Hepatoblastoma
- Hepatocellular Carcinoma (fibrolamellar Variant)
- Hepatocellular Carcinoma, Childhood
- Hepatorenal Syndrome
- Hereditary Amyloidosis
- Hereditary Angioedema
- Hereditary Ataxia
- Hereditary Coproporphyria
- Hereditary Elliptocytosis
- Hereditary Fructose Intolerance
- Hereditary Hemorrhagic Telangiectasia
- Hereditary Hyperuricemia
- Hereditary Multiple Osteochondromas
- Hereditary Neuropathy With Liability to Pressure Palsy
- Hereditary Pancreatitis
- Hereditary Spastic Paraplegia
- Hereditary Spherocytosis
- Hermansky-Pudlak Syndrome
- Herpes Simplex Encephalitis
- Herpes Zoster Ophthalmicus
- Herpetic Keratitis
- Heterotaxy
- Hirschsprung's Disease
- His Bundle Tachycardia
- Hodgkin Lymphoma
- Hodgkin Lymphoma, Childhood
- Holoprosencephaly
- Homocysteinemia
- Homocystinuria
- Homologous Wasting Disease
- Hoyeraal Hreidarsson Syndrome
- HTLV-1 Associated Myelopathy/tropical Spastic Paraparesis
- Human T-cell Leukemia Virus Type 1
- Human T-cell Leukemia Virus Type 2
- Hunter-McAlpine Syndrome
- Huntington Disease
- Hurthle Cell Thyroid Cancer
- Hydatidiform Mole
- Hydatidosis
- Hydrocephalus
- Hydrops Fetalis
- Hyper IgE Syndrome
- Hyper-IgD Syndrome
- Hyperacusis
- Hyperadrenalism
- Hypereosinophilic Syndrome
- Hyperlipidemia Type 3
- Hyperlipoproteinemia Type 1
- Hyperlipoproteinemia Type 2
- Hyperlipoproteinemia Type 5
- Hyperparathyroidism, Primary
- Hypersensitivity Vasculitis
- Hypoadrenalism
- Hypoaldosteronism
- Hypochondroplasia
- Hypocomplementemic Urticarial Vasculitis
- Hypohidrotic Ectodermal Dysplasia
- Hypokalemic Periodic Paralysis
- Hypolipoproteinemia
- Hypomagnesemia Primary
- Hypomelanotic Disorder
- Hypoparathyroidism
- Hypopharyngeal Cancer
- Hypophosphatasia
- Hypophosphatemic Rickets
- Hypopituitarism
- Hypoplastic Left Heart Syndrome
- Hypoplastic Right Heart Syndrome