Phosphate is an essential ion and plays a vital role in many physiological processes. Carpopedal spasm is known as a symptom of hypocalcemia, or rarely, hypomagnesemia. We present an unusual case of carpal spasm seen in a patient with hypophosphatemia. A fourteen year old boy was admitted with acute onset of both carpal spasm after vomiting and diarrhea. Biochemical investigation revealed only moderate hypophosphatemia without hypocalcemia. Other laboratory findings including hormone tests were normal. Carpal spasm improved with correction of hypophosphatemia. The phathophysiology of neurologic dysfunction related to hypophosphatemia is not clear yet. Careful observation of serum electrolytes including phosphate is necessary when the patient has neurologic symptoms.