Patients with atherosclerotic renal artery occlusion (RAO) effectively have only a single functioning kidney, so they constitute an ideal group in whom to study the relationship of atherosclerotic renovascular disease (ARVD) severity to renal functional outcome. Of 299 patients with ARVD who had presented to a single center over a 12-yr period, 142 (47.5%) patients with RAO were identified. There was no relationship between baseline renal function and contralateral renovascular anatomy. Patients with contralateral normal, insignificant (<50%), or significant (>50%) renal artery stenoses had baseline creatinine of 243 +/- 235, 292 +/- 197, or 210 +/- 102 micromol/L, respectively, but patients with bilateral RAO (creatinine, 540 +/- 304 micromol/L; P < 0.0001) were significantly worse. There were significant correlations between baseline GFR and both proteinuria (r = -0.32; P < 0.01) and contralateral bipolar renal length (r = 0.44; P < 0.0001). Over a mean follow-up period of 31 +/- 21 (2 to 82) mo, the overall rate of progressive renal functional decline was -4.1 ml/min per yr. Nine patients required dialysis at presentation and a further 15 (10.5%) during the course of the study. There were 85 (59.9%) deaths; median survival of the whole group was 25 mo, and 5-yr survival was 31%. Multivariate analysis indicated that low baseline GFR was the chief variable independently associated with increased probability of death or need of dialysis but that renal vascular anatomy had no prognostic impact. This study reinforces the importance of intrarenal vascular and parenchymal disease in the etiology of renal dysfunction in ARVD.