Chloride is the most abundant negative charge ion in extracellular fluid. In plasma it combines with sodium as sodium chloride and with potassium as potassium chloride. Chloride also is found with hydrogen as hydrochloric acid in the stomach. Although chloride was the first electrolyte to be easily measured, it has been considered often the least important of the major electrolytes because of its attachment to both sodium and potassium. There were lot of research and report about electrolyte imbalance, however it was difficult to find the clinical report about hypochloremia. We recently managed a patient with pyloric stenosis who was admitted to ICU with severe hypochloremic metabolic alkalosis. He was treated with hydration of normal saline and conservative management. Metabolic alkalosis and severe hypochloremia were improved and the patient was discharged on ICU 3 days.