This is the first retrospective study aimed to analyze the clinical symptoms, the etiology, the morbidity and the lethality of acute renal failure in patients over 80 years. The criterion of inclusion was the occurrence of acute renal failure defined on the basis of high plasma creatinine associated with normal kidney size in patients of this class of age who had been hospitalized in an intensive care unit between October 1971 and September 1996. In the case of a preexisting moderate nephropathy, acute renal failure was defined by an increase of plasma creatinine of at least 50% over its basal value. Three hundred and eighty-one patients over 80 years out of a total of 2,111 patients with acute renal failure were included in this study. The various etiologies and mechanisms of the disease are described. Twenty-nine% of the patients underwent dialysis. The global lethality reached 40% during the time of hospitalization. The factors significantly associated with a poor prognosis were identified as cancer essentially, but also sepsis and preexisting cardiovascular diseases. The mean survival after hospitalization was of 19 months. In summary, the frequency of admission for acute renal failure of patients over eighty in intensive care units is increasing but the rate of lethality observed is less than expected. A pattern of pathological associations leading to death in these patients cannot be defined with certitude. Therefore, the methods of renal replacement therapy available in modern intensive care units must be utilized in this class of age as it is the case in younger patients.