Background: The purpose of this prospective study is to determine whether the relationship between the weight of parathyroid tissue, serum calcium ( Ca ) and parathyroid hormone (PTH) in patients with primary hyperparathyroidism (PHPT) can serve as a reliable parameter allowing for an accurate intraoperative estimate of extent of parathyroid tissue to be removed. Method : The study included 40 patients with symptomatic sporadic PHPT due to parathyroid adenoma or hyperplasia. Preoperative measurements of total and corrected serum calcium and intact parathyroid hormone (iPTH) levels were carried out in all patients. The weight (in mg) of parathyroid tissue removed at operation was determined. The drop in iPTH and calcium levels established after surgery clearly indicates that the disorder was caused by the removed parathyroid tissue mass. The regression correlation multivariate analysis showed that the weight of the removed tissue as an independent variable correlated with iPTH and calcium levels as dependent variables. Results: The amount of parathyroid tissue correlated strongly with IPTH (r=0,549, p