The effect of renal artery stenosis on intrarenal perfusion and volume in renovascular hypertensive patients is unclear. Alterations in these attributes may ultimately be involved in deterioration of renal function. We measured whole kidney, cortical, and medullary perfusion and volume with electron beam computed tomography (EBCT) in 33 hypertensive patients, with well-preserved renal function, scheduled for renal angiography. EBCT-derived whole kidney perfusion was lower in patients with atherosclerotic renal artery stenosis (RAS; N = 20) than in fibromuscular dysplasia (FMD; N = 10) or essential hypertension (N = 28; P < 0.05), as was cortical perfusion (2.44 +/- 0.16 vs. 3.26 +/- 0.17 and 3.07 +/- 0.09 ml/min/cc tissue, respectively, P < 0.005), but medullary perfusion was similar. Whole kidney, cortical, and medullary perfusion correlated inversely with degree of stenosis in FMD, but not in atherosclerotic RAS. Renal volumes were similar. These results demonstrate that, in contrast to patients with FMD, in patients with atherosclerotic RAS the decrease in cortical perfusion is not directly related to the degree of stenosis in the main renal artery. Factors other than the stenosis itself may play a role in the pathophysiology of atherosclerotic RAS and associated renal failure.