The natural history of atherosclerotic renal artery stenosis has not been well defined, particularly when discovered in conjunction with aortic disease requiring correction. To better define the natural history of such lesions, 194 sequential aortograms in 48 patients were studied to define predictive criteria for stenoses at risk for progression. Sixty-six unsuspected atherosclerotic renal arterial stenoses were identified on the initial aortograms. Disease progressed in 42 arteries (53%), 14 bilateral and 28 unilateral. Seven arteries developed occlusion. All had stenoses averaging 80% (range 61% to 94%) noted on the most recent aortogram preceding occlusion. Risk factors including smoking, diabetes mellitus, elevated serum lipids, coronary artery disease, peripheral arterial disease, or change in blood pressure or creatinine, did not correlate with degree or rate of progression of the renal artery stenosis. A difference in kidney size, although varying inversely with degree of stenosis, was not a statistically significant marker of disease progression. This analysis suggests that identification of renal arterial stenoses that will progress is best determined by sequential aortography. Highly stenotic vessels are more prone to occlude than those less stenotic. Consequently, individuals with preocclusive lesions should benefit from prophylactic renal revascularization during aortic reconstruction.