OBJECTIVE: Our goal was to describe the course of parathyroid hormone (PTH) after surgery for primary hyperparathyroidism (PHPT). PTH levels drop to low values after parathyroidectomy for PHPT. However, in some patients, a rebound transient increase in PTH concentrations can occur. STUDY DESIGN AND SETTING: A prospective study included 72 patients who underwent surgical exploration for PHPT. A single adenoma was found in 57 patients (79.1%), 2 adenomas were found in 2 (2.7%), and parathyroid hyperplasia was found in 13 (18.05%). The postoperative PTH secretion was studied in those patients who had an adenoma excised. RESULTS: This phenomenon was noted in 18 (31.6%) patients between 4 and 12 weeks, although total calcium concentrations were normal (9.3 ± 0.6 mg/ dL). Before surgery these patients had a more remarkable hyperparathyroidism (clinical and biochemical) than the others, but differences were not significant. CONCLUSION: Postoperative increases in PTH concentration can occur after successful parathyroidectomy. These increases are transient and do not indicate persistent or recurrent disease.