Etiology, clinical course and prognosis were analysed in 346 patients with anuric/oliguric acute renal failure (ARF) treated in the Department of Nephrology, Silesian University School of Medicine in Katowice from January 1984 to December 1993. 41 of them were over 65 years of age (mean age 70.9 +/- 0.7 years) while 305 were younger (mean age 40.6 +/- 0.7 years). According to etiology patients with ARF of both groups were allocated into following subgroups: medical, urological, obstetric, rhabdomyolysis, toxic, traumatic and surgery. Total mortality was similar in both groups of patients (34.0% in older and 40.6% in younger patients respectively). Mean hospitalization time was also similar in both groups of patients with ARF (23.8 +/- 2.3 and 22.0 +/- 0.8 days respectively). Medical, urological and surgical factors were the most frequent causes of ARF in the elderly while traumatic causes and intoxications were extremely rare in these patients. Mortality in the individual etiological groups of ARF was of similarly magnitude in both examined groups. These results suggest that older age does not significantly worsen the outcome of ARF.