Hospital stays for thyroid and parathyroid surgery have decreased significantly with selected patients staying under 8 hours. Strategies to recognize hypocalcemia postoperatively vary. We examined timed postoperative calcium levels to determine how long one needs to monitor patients for hypoparathyroidism. We analyzed 120 consecutive patients having total/near-total thyroidectomy and/or parathyroidectomy between April 1998 and October 1999. Total and ionized serum calcium levels were obtained at 8, 16, and 22 hours postoperatively. Strict criteria for significant hypoparathyroidism were defined as a symptomatic patient, a total calcium value of less than 7.2 mg/dL, or an ionized calcium value of less than 1.0 mmol/L. Eighteen patients (15%) met criteria for hypocalcemia. The 8-hour ionized calcium level identified 40 per cent of those that needed supplementation. With the inclusion of the 16-hour ionized calcium value 94.5 per cent of patients who met criteria were identified. Of the 74 patients who had not previously received calcium at 22 hours after surgery only one patient with hypocalcemia was identified. Serial calcium values postoperatively add to the costs associated with an overnight hospital stay. In addition to clinical examination an ionized calcium level 16 hours postoperatively is sufficient to identify significant hypoparathyroidism in the majority of patients.