BACKGROUND: There is a paucity of information about the epidemiology of acute renal failure in Chile. AIM: To perform a prospective multicentric survey of severe acute renal failure in Chile. MATERIAL AND METHODS: All patients admitted to ten hospitals in Metropolitan Santiago, during a period of six months with severe acute renal failure, were studied. The criteria for severity was the requirement of renal replacement therapy. All patients information was gathered in special forms and the type of renal replacement therapy and evolution was registeres. RESULTS: One hundred fourteen patients were studied (65 males, age range 18 to 87 years). The calculated incidence of acute renal failure was 1.03 cases per 1000 hospital discharges. The onset was nosocomial in 79 subjects (69%) and community acquired in the rest. Renal failure was oliguric in 64 cases (56%) and in 60% of patients it had two or more causative factors. Sepsis, isolated or combined with other causes, was present in 51 of patients. Other causes included ischemia in 47%, surgery in 26%, exogenous toxicity in 25%, endocenous toxicity in 11%, acute glomerular damage in 6% and obstructive uropathy in 6%. Cardiac surgery was responsible for 47% of post operative cases of acute renal failure. Intermittent conventional hemodialysis, continuous renal replacement techniques and daily prolonged hemodialysis were used in 66%, 29% and 2% of patients, respectively. Overall mortality was 45% and it was higher in oliguric patients. Gender, age, cause or the type of therapy did not influence survival. Nine percent of surviving patients had some degree of kidney dysfunction at discharge. CONCLUSIONS: There is still a great space for prevention of severe acute renal failure in Chile, considering the main etiologies found in this study.