Abstract-Data for the effects on blood pressure of renal artery balloon angioplasty are mostly from uncontrolled studies. The aim of this study was to document the efficacy and safety of angioplasty for lowering blood pressure in patients with atherosclerotic renal artery stenosis. Patients were randomly assigned antihypertensive drug treatment (control group, nϭ26) or angioplasty (nϭ23). Twenty-four-hour ambulatory blood pressure, the primary end point, was measured at baseline and at termination. Termination took place 6 months after randomization or earlier in patients who developed refractory hypertension. In those allocated angioplasty, antihypertensive treatment was discontinued after the procedure but was subsequently resumed if hypertension persisted. Secondary end points were the treatment score and the incidence of complications. Two patients in the control group and 6 in the angioplasty group suffered procedural complications (relative risk, 3.4; 95% confidence interval, 0.8 to 15.1). Early termination was required for refractory hypertension in 7 patients in the control group. Antihypertensive treatment was resumed in 17 patients in the angioplasty group. Mean ambulatory blood pressure at termination did not differ between control (141Ϯ15/84Ϯ11 mm Hg) and angioplasty (140Ϯ15/81Ϯ9 mm Hg) groups. Angioplasty reduced by 60% the probability of having a treatment score of 2 or more at termination (relative risk, 0.4; 95% confidence interval, 0.2 to 0.7). There was 1 case of dissection with segmental renal infarction and 3 of restenosis in the angioplasty group. No patient suffered renal artery thrombosis. In unilateral atherosclerotic renal artery stenosis, angioplasty is a drug-sparing procedure that involves some morbidity. Previous uncontrolled and unblinded assessments of angioplasty overestimated its potential for lowering blood pressure.(Hypertension. 1998;31:823-829.)Key Words: renal artery obstruction Ⅲ atherosclerosis Ⅲ randomized controlled trials Ⅲ angioplasty, balloon R enal artery stenosis, mostly caused by atherosclerosis, can cause both renovascular hypertension, a form of hypertension reversible with renal revascularization, and renal insufficiency.1,2 Treatment of RAS by surgery or balloon angioplasty aims at avoiding lifelong antihypertensive treatment and progressive renal ischemia.1-3 The frequency of documented RAS varies from 0.5% to Ͼ20%, according to age 4 and the thoroughness of investigation, 5-7 and will probably increase with increasing population age and the widespread use of noninvasive screening tests. 1,[3][4][5][6][7][8] Attempts at revascularization will also increase because angioplasty, reported to be as effective as surgery 9 and recently improved by the availability of renal artery stents, 10,11 allows treatment of older and more fragile patients. The efficacy and safety of angioplasty should be objectively evaluated.12 With the exception of a randomized trial reported in abstract form, 13 however, only information based on retrospective analyses is available. 2,10,11...