Background: Primary hyperparathyroidism is caused mostly by a single adenoma and it is the most frequent cause of hypercalcemia in outpatients. Hyperplasia of the four glands and cancer are the other ethiological diagnosis. It has been postulated that the bigger and heavier an adenoma is the higher the preoperative PTH level. Objective: To evaluate a mathematical relation between adenoma estimated volume and weight and preoperative parathormone level (prPTH). Method: Retrospective analysis of 71 evaluable treated patients biopsies and preoperative PTH level. Results: A mathematical positive and weak correlation between volume, weight and preoperative PTH was obtained. This correlation was positive and strong between volumen and weight. Conclusions: In this group we found a positive and weak mathematical relation between weight, volume and preoperative PTH levels. These aspects alone are useful but only in combination with others for the correct interpretation of pre and intraoperative findings.