Purpose: To evaluate the rapid parathyroid hormone assay (rPTH) as a perioperative tool in predicting postoperative symptomatic hypocalcemia following thyroidectomy. Methods: We conducted a prospective study of 69 patients undergoing total or completion thyroidectomy. Rapid PTH levels were obtained preoperatively, intraoperatively, and postoperatively upon arrival in the postanesthesia care unit (PACU). All patients were closely monitored postoperatively for the development of symptomatic or asymptomatic hypocalcemia. Results: Of 60 patients (25%) undergoing thyroidectomy, 15 developed hyypocalcemia, 7 (11.7%) were symptomatic, and 8 (13.3%) asymptomatic. An intraoperative rPTH level less than 12 pg/mL was 71% sensitive and 95% specific for predicting postoperative symptomatic hypocalcemia, whereas a PACU rPTH level less than 12 pg/mL was 100% sensitive and 92% specific. A greater than 75% decline in preoperative rPTH level when measured intraoperatively was 71% sensitive and 86% specific, whereas a greater than 75% decline in rPTH level in the PACU was 100% sensitive and 88% specific for predicting symptomatic hypocalcemia. Conclusions: The rPTH assay is a highly accurate and effective tool for predicting symptomatic hypocalcemia immediately after thyroidectomy. Routine utilization of this assay is recommended, because it will allow safe and timely discharge of normocalcemic patients and the early identification of patients requiring treatment of postthyroidectomy hypocalcemia.