Renal failure is frequently considered an ominous development after injury, but its impact on outcome is poorly understood. Renal dysfunction or failure can be defined in many ways, such as elevated serum creatinine or the need for dialysis. The best method to characterize renal dysfunction however, is not known. To determine which definition of renal dysfunction correlates best with outcome, we retrospectively analyzed all injured patients from 1994 to 2000 who had an Injury Severity Score > or =14 and a hospital length of stay >2 days for the development of renal impairment. One hundred sixty-seven patients (4%) developed a serum creatinine > or =2.0 mg/dL and 49 patients required dialysis. Patients with renal dysfunction were older, suffered from more comorbid medical problems, were more seriously injured, and were more likely to have been in shock. A serum creatinine > or =2.0 mg/dL, the maximum creatinine level, and need for dialysis, were highly correlated with death, and the total number of dialysis treatments was not. All measures of renal dysfunction correlated relatively poorly with length of stay. These data demonstrate that the simple measure of serum creatinine > or =2.0 mg/dL is associated with a significantly increased likelihood of death in injured patients and is a stronger predictor than other common indicators of renal impairment.