The efficacy of angiotensin converting enzyme (ACE) inhibitors in treatment of renovascular disease has been controversial. It has been reported that patients with incidental atherosclerotic renal artery stenosis (ARAS) are sometimes treated with ACE inhibitors before being considered for renal revascularization. This study was designed to describe the frequency and the characteristics of patients with incidental ARAS, and to examine the frequency of ACE inhibitor usage in such patients. We studied a cohort of consecutive patients undergoing abdominal aortography at the time of cardiac catheterization. Patients were stratified and compared based on the presence and severity of ARAS. ARAS (greater than or equal to50%) was present in 146 (17.0%) of 859 evaluable patients. Factors independently related to the presence of ARAS were age (odds ratio (OR)=1.07, p<0.001), severity of coronary artery disease (OR=2.13, p<0.001) and peripheral vascular disease (OR=1.79, p=0.021). Among all patients with ARAS, the percentage of ACE inhibitor usage was 74.7% (109/146). Among patients with severe ARAS, moderate ARAS, mild ARAS, insignificant ARAS and normal renal arteries, the percentage of ACE inhibitor usage was 85.7% (95% confidence interval (Cl): 69-100%), 82.9% (95% Cl: 71-95%), 68.5% (95% Cl: 59-78%), 68.6% (95% Cl: 55-82%) and 53.9% (95% Cl: 50-58%), respectively (contingency coefficient=0.17, p<0.001). In patients with severe ARAS, ACE inhibitor use, calcium channel blocker use and diuretic use were shown to correlate significantly with serum creatinine levels after controlling for potential confounding factors. In this study, ACE inhibitors were used commonly in patients with incidental ARAS; the frequency of ACE inhibitor use correlated with the severity of ARAS.