- Haemophilus ducreyi
- Haemophilus influenzae
- Haemophilus influenzae type b vaccine
- Hair bezoars (trichobezoars)
- Hair loss
- Hair tourniquet syndrome
- Hallermann-Streiff syndrome
- Hamartomas
- Hand, foot, and mouth disease
- Hand-Schüller-Christian syndrome
- Hartnup syndrome
- Hashimoto-Pritzker syndrome
- Hashimoto thyroiditis
- Headache
- Head and neck infections, anaerobic
- Head banging
- Head lice
- Head trauma
- Hearing loss
- Heart failure
- Heart–lung transplantation, for cardiomyopathy
- Heart rate
- Heart transplantation
- Heat cramps/spasms
- Heat edema
- Heat exhaustion
- Heat intolerance, in cystic fibrosis
- Heat stroke
- Heat syncope
- Heat tetany
- Heavy metal poisoning
- Heiner syndrome
- Heinz body hemolytic anemia
- Helicobacter pylori
- Heliox (helium/O 2 )
- HELLP syndrome
- Hemangioblastoma
- Hemangioma
- Hemangiopericytoma
- Hematemesis
- Hematochezia
- Hematoma
- Hematopoietic stem cell transplantation (HSCT)
- Hematuria
- Hemifacial microsomia
- Hemifacial spasm
- Hemi-Fontan procedure
- Hemimegalencephaly
- Hemiplegic migraine
- Hemochromatosis
- Hemoglobin H disease
- Hemoglobinopathies
- Hemolysis
- Hemolytic anemia
- Hemolytic disease of fetus or newborn (HDFN)
- Hemolytic uremic syndrome (HUS)
- Hemophagocytic lymphohistiocytosis (HLH)
- Hemophagocytic syndrome
- Hemophilia
- Hemoptysis
- Hemorrhagic cystitis
- Hemorrhagic stroke
- Hemorrhoids, in portal hypertension
- Hemosiderosis, pulmonary
- Henoch-Schönlein purpura (HSP)
- Hepatic abscess
- Hepatic decompensation
- Hepatic encephalopathy
- Hepatic failure
- Hepatic fibrosis
- Hepatic mass
- Hepatic toxicity, in cancer therapy
- Hepatic venous outflow obstruction
- Hepatitis
- Hepatitis A
- Hepatitis A vaccine
- Hepatitis B
- Hepatitis B immune globulin
- Hepatitis B vaccine
- Hepatitis C
- Hepatitis D
- Hepatitis E
- Hepatoblastoma
- Hepatocellular carcinoma
- Hepatocyte transplant
- Hepatomegaly
- Hepatoportoenterostomy
- Hepatopulmonary syndrome
- Hepatorenal syndrome
- Hereditary angioedema (HAE)
- Hereditary ectodermal dysplasia
- Hereditary elliptocytosis
- Hereditary fructose intolerance
- Hereditary glomerulonephritis
- Hereditary hemochromatosis
- Hereditary hemorrhagic telangiectasia
- Hereditary multiple exostoses
- Hereditary spherocytosis
- Hermansky-Pudlak syndrome
- Hernia
- Herniated disc
- Herpangina
- Herpes gladiatorum
- Herpes simplex virus (HSV)
- Herpes zoster
- Herpetic gingivostomatitis
- Herpetic whitlow
- Heterotaxy syndrome
- Heterotopia
- Hexoaminidase deficiency
- Hiccups
- High-altitude cerebral edema (HACE)
- High-altitude pulmonary edema (HAPE)
- Highly active antiretroviral therapy (HAART)
- Hip
- Hip dysplasia
- Hirschsprung disease
- Hirsutism
- Histamine 2 antagonists
- Histiocytosis
- Histiocytosis X
- Histoplasmosis
- HIV
- Hives
- Hodgkin lymphoma
- Holocarboxylase synthetase deficiency
- Holoprosencephaly
- Holter monitor
- Holt-Oram syndrome
- Home cardiorespiratory monitoring
- Homocystinuria
- Honey
- Hookworms
- Hordeolum
- Hormone therapy
- Horner syndrome
- Horseshoe abscess
- Horseshoe kidney
- HSCT
- Human bites
- Human granulocytic anaplasmosis (HGA)
- Human herpesvirus 6
- Human herpesvirus 7
- Human immunodeficiency virus (HIV) infection
- Human monocytic ehrlichiosis (HME)
- Human papillomavirus (HPV)
- Human papillomavirus (HPV) vaccine
- Human rabies immune globulin (HRIG)
- Hungry bone syndrome
- Hunter syndrome
- Huntington disease
- Hurler syndrome
- HUS
- Hutchinson-Gilford progeria syndrome
- Hyaline membrane disease
- Hydatid cysts
- Hydration
- Hydroa aestivale
- Hydroa vacciniforme
- Hydrocele
- Hydrocephalus
- Hydrocolpos
- Hydronephrosis
- Hydrops fetalis
- Hydroureteronephrosis
- Hydroxocobalamin
- Hyperaldosteronism
- Hyperammonemia
- Hyperbaric oxygen treatment, for carbon monoxide poisoning
- Hyperbilirubinemia
- Hypercalcemia
- Hypercalcemia of malignancy
- Hypercalciuria
- Hyperchloremic acidosis
- Hypercholesterolemia
- Hyperekplexia
- Hypereosinophilic syndrome (HES)
- Hyperglycemia
- Hyperglycinemia, nonketotic
- Hyperimmunoglobulin D (IgD) syndrome
- Hyperimmunoglobulinemia E syndrome (HIES)
- Hyperimmunoglobulin M (IgM) syndromes
- Hyperinsulinism
- Hyperkalemia
- Hyperleukocytosis
- Hyperlipidemia
- Hypernatremia
- Hyperopia
- Hyperoxaluria
- Hyperoxia test
- Hyperparathyroidism
- Hyperparathyroidism-jaw tumor syndrome
- Hyperphosphatemia
- Hyperpigmentation, acne and
- Hyperprolactinemia
- Hypersensitivity reaction, with food
- Hypersomnolence, in floppy infant syndrome
- Hypersplenism
- Hypertension
- Hypertensive emergencies
- Hypertensive urgencies
- Hyperthermia
- Hyperthyroidism
- Hypertriglyceridemia
- Hypertrophic cardiomyopathy (HCM)
- Hypertropia
- Hyperuricosuria
- Hypervolemic hyponatremia
- Hypnagogic hallucinations
- Hypoalbuminemia
- Hypocalcemia
- Hypochloremia, in pyloric stenosis
- Hypocortisolism
- Hypogammaglobulinemia
- Hypoglycemia
- Hypogonadism
- Hypogonadotropic hypogonadism
- Hypokalemia
- Hypokalemic periodic paralysis
- Hypomagnesemia
- Hypomelanosis of Ito
- Hypomelanotic macules
- Hyponatremia
- Hyponatremic encephalopathy
- Hypoparathyroidism
- Hypophosphatasia, infantile
- Hypophosphatemia
- Hypophosphatemic disorders
- Hypophysitis
- Hypopituitarism
- Hypoplastic left heart syndrome (HLHS)
- Hypoplastic thorax syndrome
- Hypopnea
- Hypospadias
- Hyposplenia
- Hypotelorism
- Hypotension
- Hypothermia
- Hypothermia therapy
- Hypothyroidism
- Hypotonia
- Hypoventilation
- Hypovolemia
- Hypovolemic hyponatremia
- Hypovolemic shock
- Hypoxemia
- Hypoxemia-induced pulmonary hypertension
- Hypoxia
- Hypoxic-ischemic encephalopathy (HIE)
- Hypsarrhythmia