A woman aged 33 years presented hypokalemia and hypomagnesemia associated with renal potassium and magnesium wasting. Her mean 24-hour urinary calcium excretion was strikingly low despite normocalcemia, normal creatinine clearance, normal serum PTH and calcitriol. Normal distal fractional chloride reabsorption [CH2O/(CH2O + CCl)] was noted during water load but was reduced during hypotonic saline infusion. In response to intravenous furosemide (1 mg/kg), the patient showed significant increments in sodium, chloride and magnesium excretion as well as abolition of hypocalciuria. The association of renal calcium transport from magnesium transport together with exaggerated natriuresis after furosemide suggests the presence of a defect in the distal tubule rather than in the loop of Henle. We propose that our patient is affected by the syndrome of primary renotubular hypomagnesemia-hypokalemia with hypocalciuria, known as Gitelman's syndrome.