The annual incidence of acute renal failure (ARF) in the general population seems close to 150 per million inhabitants. For the past 20 years, there has been an increase in ARF of medical origin and a simultaneous decrease in surgical, traumatic and obstetrical ARF. Drug-induced ARF accounts for 20% of total cases. Factors of poor prognosis include a poor previous health status, the presence of oliguria, cardiac or respiratory insufficiency, sepsis, coma, a need for mechanical ventilation and, most importantly, the number of failing organs. The three main severity scoring systems used are SAPS, APACHE II and OSF. The predictive value of these scoring systems seems acceptable provided the data are collected when ARF is diagnosed and not on the patients' admission. After years, the overall survival rate does not exceed 30% to 50%. Full renal recovery is observed in 1/3 to 2/3 of surviving patients and varies according to the type of nephropathy. The social and financial consequences of these results emphasize the importance of preventing ARF, especially in its iatrogenic form.