Post-thyroidectomy parathyroid hormone (PTH) levels have been used to predict hypocalcemia. The goal of this study was to determine whether selective supplementation for post anesthesia care unit (PACU) PTH < 15 mg/dL reduced hypocalcemia compared to observation or routine supplementation. Controlled cohort study of thyroidectomy patients, with chart review. Chart review of total or completion thyroidectomy patients in an academic setting. The control group consisted of 124 subjects. The selective supplementation group consisted of 169 subjects with routine PACU PTH testing. The routine supplementation group consisted of 155 subjects with immediate postoperative calcium and vitamin D supplementation. The control group received supplementation for hypocalcemia (calcium < 8.0 mg/dL). The selective PTH group received calcium and vitamin D supplementation for PACU PTH < 15 mg/dL or hypocalcemia. The routine supplementation group received oral calcium and calcitriol supplementation immediately after surgery. Four separate postoperative day 1 (POD1) outcome measures were evaluated: 1) mean serum calcium; 2) rate of hypocalcemia < 8 mg/dL; 3) rate of significant hypocalcemia < 7.5 mg/dL; and 4) rate of hypercalcemia > 10 mg/dL. Mean serum calcium was lower and the rate of hypocalcemia was higher in the control group than the selective PACU PTH group on POD1 (8.2 vs 8.6 mg/dL, P < 0.0001, and 35% vs 14%, P < 0.0001, respectively). Mean serum calcium was higher (8.9 vs 8.6 mg/dL, P < 0.0001) and the rate of hypocalcemia lower in the routine supplementation group than in the selective group. However, the rate of hypercalcemia was higher in the routine supplementation group than in the selective group (4.5% vs 0%, P = 0.006). Routine PTH testing and supplementation for patients with hypoparathyroidism reduced the proportion of patients experiencing hypocalcemia. However, supplementation for intraoperative PTH < 15 mg/dL had a higher rate of hypocalcemia than routine supplementation, but with a lower rate of hypercalcemia.