OBJECTIVES: Hypoparathyroidism is the most frequent complication of thyroidectomy. The incidence rates of temporary and permanent postoperative hypoparathyroidism vary from 7 to more than 60% and from 0 to 9%, respectively. DESIGN: The aim of the study has been to evaluate the incidence of hypoparathyroidism and clinical manifestations of hypocalcaemia after total thyroidectomy, as well as assess factors that affect the frequency of the symptomatic hypocalcaemia, and benefits resulting from the measurement of parathyroid hormone (PTH) concentration on the first day after thyroidectomy. SETTING: The studied group consisted of 330 patients after total thyroidectomy, while the control group consisted of 86 patients who underwent total resection of one lobe only or subtotal thyroidectomy. RESULTS: Based on the measurements of serum PTH concentration on the first day after total thyroidectomy, postoperative hypoparathyroidism was diagnosed in 48% of patients. After total thyroidectomy, the frequency of clinical symptoms of hypocalcaemia was twice less than the incidence of hypoparathyroidism confirmed by biochemical testing. Total thyroidectomy occurred to be an independent factor of the increased risk of postoperative hypoparathyroidism. This risk was even higher in the cases widened by lymphadenectomy, and among patients with Graves' disease. In the group of patients with decreased serum PTH concentration the occurrence of clinical symptoms of hypocalcaemia significantly depended on serum PTH concentration - patients with lower PTH levels reported paresthesias more frequently. CONCLUSIONS: Serum PTH levels below 5 pg/ml seems to be a good prognostic factor of the occurrence of hypocalcaemia symptoms. The information about low PTH concentration allows to start the pharmacotherapy faster and avoid clinical manifestation of hypocalcaemia.