A 4-month-old male infant was referred to our center with clinical signs and symptoms of severe dehydration without fever, diarrhea, vomiting, or respiratory symptoms. The patient had a history of two similar episodes at 1.5 and 2 months of age without any known underlying cause. In each attack the patient was hospitalized and improved with management of dehydration and electrolyte imbalance. The main abnormal laboratory findings on all admissions were: hypochloremic, hyponatremic, hypokalemic metabolic alkalosis. Sweat chloride was checked at all admissions, and was found to be highly abnormal at the last admission.