OBJECTIVE Acute renal failure (ARF) is associated to multiple organ failure (MOF) in critically ill patients and its mortality is high. The main objective was to evaluate the outcome of critically ill patients with ARF and MOF treated with continuous venovenous hemodiafiltration (CVVHDF). METHODS Retrospective and observational study on critically ill patients. METHODS Medical-surgical Intensive Care Unit (ICU) in a University Hospital of Girona. METHODS Patients admitted in ICU that developed ARF and MOF and were treated with CVVHDF. METHODS We collected data on demographic, and severity and organic dysfunction scores (SOFA). To study the risk factors for mortality, a comparative and multiple regression statistical analysis was performed, with the main effect of the study being mortality at 30 days. RESULTS We studied 139 patients. The most frequent predisposing factors were hypotension (98%) and sepsis (82%). the most frequently affected organs were cardiocirculatory (94%) and respiratory (47%) associated to ARF. Mean SOFA score was 11.4 + or - 2.7 points. Survival was better in traumatic and in non-oliguric patients. The 30-day mortality was 61% and the logistic regression analysis showed that age > or = 60 years [OR=3.3 (95% CI 95=1.5-7.0)] and SOFA score > or = 11 points [OR=2.5 (95% CI=1.1-5.3)] were related to mortality. CONCLUSIONS The mortality rate of critically ill patients with acute renal failure and multiple organ failure remains high. Traumatic and non-oliguric patients have a better survival. Age > or = 60 years and SOFA > or = 11 points were independent risk factors associated with mortality.