BACKGROUND: Hypocalcemia is the most frequent complication following total thyroidectomy. This prospective study examines the predictive value of parathyroid hormone (PTH) levels measured 24 hours after surgery. MATERIAL AND METHODS: A total of 1006 consecutive patients (mean age, 54.8 years; female/male ratio, 4/1) underwent total thyroidectomy for benign or malignant thyroid from January 1995 to November 2003. Serum calcium, phosphorus, and PTH were measured preoperatively and at 24 hours after surgery. All patients underwent preoperative examination to assess cord motility. RESULTS: A total of 253 (25.1%) patients presented with hypocalcemia demonstrated by clinical and laboratory findings. In 101 cases the hypocalcemic syndrome manifested after 24 to 36 hours whereas in 5 of 101 cases, symptom onset was between 48 and 72 hours. Serum calcium levels lower than 7.5 mg/dL were recorded in all the 101 cases. In 239 of 253 cases serum calcium returned to normal values within 7 days following surgery. PTH at 24 hours was below normal levels in 49 of the 101 patients but was within normal limits in 52 cases. The incidence of hypocalcemia was higher in patients undergoing surgery for malignant thyroid ( P < 0.05). CONCLUSIONS: We do not consider PTH levels at 24 hours postoperatively as predictive of hypocalcemia.