Natural history and outcome of percutaneous transluminal renal angioplasty (PTRA) in renovascular hypertension (RVH) were assessed retrospectively in 52 patients in whom 62 PTRAs were successfully performed. Complications were observed in 16 patients: prolonged and extensive arterial spasms in eight, severe intimal dissection of the main renal artery in five, arterial thrombosis at the site of PTRA in two and acute deterioration of renal function in one. All the complications cleared up with medical treatment except for one major dissection occluding the distal branches, which required surgery. According to the Co-operative Study, after 1-5 years of follow-up, 21 patients (40.4%) were cured, 27 (51.9%) improved and four (7.7%) did not improve. The long-term results on blood pressure in both uncomplicated and complicated cases were better in fibrodysplasia (61.5% cured, 34.6% improved and 3.8% not improved) than in atherosclerosis (17.4% cured, 69.6% improved and 13% not improved). In the last 21 PTRAs performed, in which verapamil (200-1500 micrograms) was given as a bolus injection into the stenotic artery before dilatation, the complication rate was significantly lower. It is concluded that PTRA is an effective treatment for RVH; complications occurred in 25.8% of PTRAs and resulted in poor control of blood pressure in atherosclerosis but not in fibrodysplasia; premedication with verapamil into the stenotic renal artery reduced the complication rate.