Background: Symptomatic hypocalcemia, the most common complication of total thyroidectomy, can lead to postoperative emergency room visits for laboratory testing and intravenous calcium infusion. A method to identify patients reliably at risk for postoperative hypocalcemia could allow prophylactic treatment to avoid this. We hypothesized that quick parathyroid hormone testing within 4 hours of thyroidectomy and a protocol to treat parathyroid-hormone-deficient patients would reduce symptomatic hypocalcemia, eliminating the need for emergency room visits. Methods: After January 1, 2006, 271 consecutive patients underwent total thyroidectomy with postoperative parathyroid hormone testing (group 1). Patients with parathyroid hormone levels <10 pg/mL were treated according to a newly instituted protocol with 0.25-ug calcitriol twice daily and 2-6 g of calcium carbonate daily for 1 week. Patients with parathyroid hormone levels ≥10 pg/mL were treated with calcium only. Group 2 consisted of 100 consecutive patients who underwent total thyroidectomy prior to 2006 without parathyroid hormone testing and were treated according to surgeon preference and serum calcium levels. Results: Patients in the 2 groups were similar with regard to age, sex, and thyroiditis. However, patients in group 1, who had parathyroid hormone testing, had greater postoperative calcium levels (P < .005). Also, patients in group 2 had a higher incidence of malignancy (P = .04). Importantly, patients in group 1 had a lesser incidence of symptomatic hypocalcemia (7% vs 17%; P = .005). Furthermore, the number of patients who made visits to the emergency room was less in patients who had parathyroid hormone testing compared with those who did not (1.8% vs 8.0%; P = .008). Conclusion: Postoperative parathyroid hormone testing reliably identifies patients at risk for hypocalcemia after thyroid surgery. Moreover, parathyroid hormone testing and calcitriol administration to patients at risk decreases the incidence of hypocalcemia and associated emergency room visits after total thyroidectomy. Therefore, patients with postoperative serum parathyroid hormone levels <10 pg/mL after thyroid surgery should be treated with calcitriol and calcium to prevent symptomatic hypocalcemia. © 2010 Mosby, Inc. All rights reserved.