Hypocalcemia persists as a problem after thyroidectomy. We reviewed our experience with 245 thyroidectomies to define the spectrum of hypocalcemia, elucidate the mechanisms of hypocalcemia, and formulate a rational basis for its management. Postoperative hypocalcemia occurred in 8.6% of all patients undergoing thyroid surgery with incidence the highest in patients with total thyroidectomy for cancer (28%) and those with subtotal thyroidectomy for thyrotoxicosis (23%). Incidence was low in patients having subtotal thyroidectomy for other diseases (1.5%) and lobectomy (0%). The high incidence of hypocalcemia following subtotal thyroidectomy for thyrotoxicosis but not for other diseases suggests that a mechanism other than removal or damage of the parathyroids is responsible for the hypocalcemia. This may well be thyrotoxic osteodystrophy. This hypocalcemia usually occurs early, is of moderate degree, and is transient. Management includes calcium gluconate for acute symptoms and calcium lactate with vitamin D2 for chronic symptoms.