Inherited classic Bartter syndrome (cBS) is an autosomal recessive renal tubular disorder resulting from inactivating mutations in the asolateral chloride channel (C1C-Kb) and usually presents in early infancy or childhood with mild to moderate hypokalemia. Profound hypokalemic paralysis in patients with cBS is extremely rare, especially in middle age. A 45-year-old Chinese female patient was referred for evaluation of chronic severe hypokalemia despite regular K+ supplementation (1 mmol/kg/d). She had had two episodes of muscle paralysis due to severe hypokalemia (K+ 1.9 - 2.1 mmol/l) in the past 3 years. She denied vomiting, diarrhea, or the use of laxatives or diuretics. Her blood pressure was normal. Biochemical studies showed hypokalemia (K+ 2.5 mmol/l) with renal potassium wasting, metabolic alkalosis (HCO3- 32 mmol/l), normomagnesemia (Mg2+ 0.8 mmol/l), hypercalciuria (calcium to creatinine ratio 0.5 mmol/mmol; normal < 0.22 mmol/mol), high plasma renin activity, but normal plasma aldosterone concentration. Abdominal sonography revealed neither renal stones nor nephrocalcinosis. Acquired causes of cBS such as autoimmune disease and drugs were all excluded. Molecular analysis of the CLCNKB gene, encoding ClC-Kb, and SLC12A3, encoding the thiazide-sensitive sodium chloride cotransporter (NCC), revealed compound heterozygous mutations in CLCNKB (L335P and G470E) inherited from her parents; her SLC12A3 was normal. These two mutations were not identified in 100 healthy subjects. Her plasma K+ concentration rose to 3 - 3.5 mmol/l after the addition of spironolactone. Inherited cBS may present with hypokalemic paralysis and should be considered in adult patients with hypokalemia and metabolic alkalosis.