Abstract. Mortality rates in acute renal failure remain extremely high, and risk-adjustment tools are needed for quality improvement initiatives and design (stratification) and analysis of clinical trials. A total of 605 patients with acute renal failure in the intensive care unit during 1989-1995 were evaluated, and demographic, historical, laboratory, and physiologic variables were linked with in-hospital death rates using multivariable logistic regression. Three hundred and fourteen (51.9%) patients died in-hospital. The following variables were significantly associated with in-hospital death: age (odds ratio [OR], 1.02 per yr), male gender (OR, 2.36), respiratory (OR, 2.62), liver (OR, 3.06), and hematologic failure (OR, 3.40), creatinine (OR, 0.71 per mg/dl), blood urea nitrogen (OR, 1.02 per mg/dl), log urine output (OR, 0.64 per log ml/d), and heart rate (OR, 1.01 per beat/min). The area under the receiver operating characteristic curve was 0.83, indicating good model discrimination. The model was superior in all performance metrics to six generic and four acute renal failurespecific predictive models. A disease-specific severity of illness equation was developed using routinely available and specific clinical variables. Cross-validation of the model and additional bedside experience will be needed before it can be effectively applied across centers, particularly in the context of clinical trials.Acute renal failure (ARF) in critically ill patients is associated with a distressingly high mortality rate (1-3). Despite improvements in intensive care and dialytic technology, particularly with continuous renal replacement therapies, we have not observed meaningful improvements in patient survival over the past three decades (4 -8). In most series, more than 50% of patients with hospital-acquired ARF die before hospital discharge; of those who survive, between 10 and 33% require long-term dialysis (9 -11).Over the past decade, several clinical trials have been conducted, aiming to reduce ARF-associated mortality (12)(13)(14). Most of these studies have unfortunately proved unsuccessful, including relatively large, well-designed trials using pharmacologic agents with strong preclinical data (e.g., atrial natriuretic peptide [ANP]). Among the difficulties in design and analysis of clinical trials in ARF are the lack of a standardized definition of ARF, the heterogeneity of ARF, comorbidity and severity of illness directly influencing mortality, and large variations in the process of care. -24). Moreover, the timing of evaluation (e.g., consultation, initial dialysis procedure) and the population to which the index was applied (e.g., all patients with ARF, only dialyzed patients, etc.) have differed across studies. To prepare for future clinical trials in ARF, it is essential that valid, generalizable models for risk adjustment be developed, both for stratification in patient selection and for covariate adjustment in the event of imbalanced randomization.We evaluated 851 consecutive cases of ARF in the intensive...