Postoperative hypocalcemia is the most common complication after thyroidectomy. Postoperative supplementation with calcium and calcitriol reduces its occurrence; however, prophylactic preoperative supplementation has not been studied systematically. The primary objective of this study was to determine whether pre- and postoperative calcium and calcitriol supplementation reduces postoperative hypocalcemia after total thyroidectomy compared with postoperative supplementation alone. We conducted a single-institution prospective randomized trial enrolling 82 patients undergoing total thyroidectomy from July 2017 through May 2019. Those undergoing partial thyroidectomy or concurrent planned parathyroidectomy were excluded. The intervention group started calcitriol 0.25 μg po bid and calcium carbonate 1,500 mg po tid 5 days preoperatively and continued postoperatively. The control group started these medications postoperatively. The primary end point was clinical or biochemical hypocalcemia. Secondary outcomes were postoperative calcium levels, need for intervention, length of stay, and readmission. Thirty-eight patients were randomized to the intervention group and 44 to the control group. There were 12 episodes of hypocalcemia; 5 (13.2%) in the intervention and 7 (15.9%) in the control group (p = 0.76). No differences were found in secondary outcomes; including postoperative calcium levels at each measured time point, need for intervention (n = 10 26.3%, n = 15 34.1%; p = 0.48), length of stay (mean SD 32.3 15.6 hours, 30.7 10.5 hours; p = 0.6), or readmissions (n = 0 0.0%, n = 3 6.8%; p = 0.24). Starting supplementation with calcium and calcitriol preoperatively does not reduce postoperative hypocalcemia compared with postoperative supplementation alone after total thyroidectomy. These findings do not support the practice of routine calcium and calcitriol supplementation before total thyroidectomy. Display omitted