Of 51 patients with primary hyperparathyroidism (2 patients with MEN, Type 1 clinical symptomatology, diagnostic procedures, differential diagnosis, operative strategy and long-term results are being reported. Aside from clinical findings and radiologic signs in our hands determination of the ionized serum calcium fraction, results of chrest bone biopsies and parathormone determinations are best parameters to substantiate the diagnosis of PHPT. Parathormone radioimmunassay determination is very helpful in localizing the adenoma, especially in cases of reoperations. Five patients were seen in acute hypercalcemic crises, in which emergency operations are absolutely indicated. Postoperative hypercalcemia and recurrencies were observed in 3.9%. Successful extirpation of parathyroid adenomas (15% multiple adenomas were found) is the therapy of choice in PHPT, only in cases with hyperplasia subtotal parathyroidectomy is indicated.