Bilateral clamping of renal pedicles during 60, 75 or 90 min was used to characterize the evolution of ischemic acute renal failure (ARF) in prepubertal rats. To verify the existence of age-conditioned differences in the evolution of ARF, adult rats were exposed to 40, 60 or 75 min of clamping. After 7 days, survival rate was significantly better in young than adult rats for identical times of clamping (89 vs. 35% for 60 min and 69 vs. 35% for 75 min). Young rats largely died within the first 24 h following ischemia while the risk of death extended until the 4th day after ischemia in adult rats. Peak values of serum urea nitrogen and creatinine were observed on the 1st and 3rd day after ischemia in young and adult rats, respectively. In young rats, these markers of renal function returned to normal on days 5 and 6 whereas they remained elevated at the end of the study in adult animals. Growth curves of young rats paralleled those of sham-operated animals from the 3rd day of clamping whereas adult rats did not even reach the initial weight at the end of the study. Analysis of kidneys obtained 7 days after clamping revealed more severe histopathological lesions in adult rats as well as a higher proliferative activity (10–40 times the value of sham-operated animals versus 2–4 times the control value in young rats). Our findings indicate that kidneys from young rats are more resistant to ischemia and recover more quickly from the ischemic insult. Therefore, the experimental model of ischemic ARF is clearly different in young and adult rats.