BACKGROUND: We prospectively evaluated the possibility to make an early prediction of postthyroidectomy hypocalcemia by postoperative intact parathyroid hormone (iPTH) measurements. METHODS: Fifty-three consecutive patients who underwent bilateral thyroid resection were included; iPTH was measured preoperatively, at the end of the surgical procedure, and at 2, 4, 6, 24, and 48 hours after the operation. Patients who had hypocalcemia (serum total calcium, <8.0 mg/dL) were compared with normocalcemic patients. RESULTS: Sixteen patients experienced hypocalcemia. Six patients experienced symptoms. No significant difference was found between hypocalcemic and normocalcemic patients concerning demographic, pathologic, and preoperative laboratory data, surgical procedure, and intraoperative findings. Postoperative iPTH levels were reduced in hypocalcemic patients at the end of the procedure and at 2, 4, 6, 24, and 48 hours after the operation ( P < .001). IPTH levels below the normal range (<10 pg/mL) at 4 and 6 hours after the operation correctly predicted postoperative hypocalcemia and symptoms in all but 1 patient with a self-limiting, asymptomatic hypocalcemia (serum calcium concentration, 7.8 mg/dL) (specificity, 100%; sensitivity, 94%; overall accuracy, 98%). CONCLUSIONS: One single iPTH measurement reliably can predict, early after thyroidectomy, which patients are prone to clinically relevant postoperative hypocalcemia and necessitate supplementation treatment and which patients are eligible for a safe early discharge.