Hypocalcaemia is a complication of parathyroidectomy. We retrospectively analyzed data on patients who underwent parathyroidectomy for primary hyperparathyroidism (pHPT) to identify predictive factors for severe postoperative hypocalcaemia. Since 2004 we performed 87 parathyroidectomies for pHPT. We divided the patients into two groups: subjects who presented with postoperative hypocalcaemia (group B) or otherwise (group A). We looked for a correlation between several variables and the incidence of postoperative hypocalcaemia. The median calcemia in group B (19 patients) was 6.9 mg/dL on the first postoperative day and 7.6 mg/dL on the third day. We observed hypocalcemia related clinical symptoms in every patient. In all 19 cases the reduction of intraoperative parathyroid hormone above 85 per cent after parathyroidectomy was related to the development of severe postoperative hypocalcaemia (P = 0.042). We found that the reduction of intraoperative parathyroid hormone over 85 per cent after parathyroidectomy can be considered a reliable predictive factor of postoperative hypocalcaemia after parathyroidectomy for primary hyperparathyroidism.