Some authors have reported acute impairment of renal transplant function after parathyroidectomy (PTx). Since 1996 PTx has been performed in 22 renal transplant recipients (follow-up, 24.2 +/- 15 months; serum creatinine concentration (SCr) pre-PTx, 1.26 +/- 0.4 mg/dL). We analyzed the serum levels of immunoreactive parathyroid hormone, calcitriol, calcium, phosphate, alkaline phosphatase, SCr, and hemoglobin, as well as proteinuria, blood pressure, and immunosuppressive treatment at several times: before PTx and at 7 days, 1 month, and then every 3 months post-PTx. After PTx we observed acute renal function deterioration until the third post-PTx month, when SCr levels returned to baseline values. We found no changes in blood pressure, although there was a trend toward a reduced dosage of antihypertensive drugs. We compared the patients who showed more significant increases (>30% from baseline) in SCr (group A, n = 7) with those who did not (group B, n = 15). Group A had higher SCr levels pre-PTx. We observed no other significant differences, either pre-PTx or post-PTx. In 2 patients in group A, SCr returned to baseline at the third month after PTx, but in the other 5 the renal function impairment persisted. Taking into account this risk and that severe hyperparathyroidism does not revert after transplantation, it would seem more appropriate in such cases to perform PTx while the patient is on the waiting list. The causes of this renal functional impairment are not clear, but the patients who showed worse deterioration also had a worse renal function pre-PTx.