A 31-year-old woman had a history of fatigue and hypokalemia and metabolic alkalosis and hypocalciuria. The patient had a subtotal thyroidectomy and denied ingestion of diuretic medication. Her clinical and laboratory findings were consistent with Gitelman's syndrome. Normal blood pressure, hypokalemic metabolic alkalosis, hypocalciuria were present. She confessed to us that she had been taking a pill due to constipation for 7 years. She was afraid that her husband know it. But we don't know the reason why she had concealed it Surreptious ingestion of diuretics must be excluded in any adult patient in whom a diagnosis of Bartter's or Gitelman's syndrome is considered.