A rare autosomal recessive condition, with prevalence of 1 in 1 000 000, leading to a defect in sodium chloride reabsorption in the medullary thick ascending limb of the loop of Henle that often presents in childhood and is characterized by hypokalemia, metabolic alkalosis, hyperreninemia due to mild chronic volume depletion, hyperaldosteronism, and normal to slightly decreased serum magnesium level. Other clinical symptoms include production of dilute urine due to decreased urinary concentrating ability, increased urinary calcium excretion, growth retardation, and intellectual disability.

Bartter syndrome is classified as types I-IV. In addition, there is a phenotype called type V (also known as autosomal dominant hypocalcemia, or autosomal dominant hypoparathyroidism). Types I, II, IV, and IVb usually present in earlier life and with more severe disease, and types III and V present later in life with milder symptoms.

See also Gitelman Syndrome.