BACKGROUND As care of the critically ill patient has improved and definitions of organ failure have changed, it has been observed that the incidence of organ failure and the mortality associated with organ failure appear to be decreasing. In addition, many early studies included large heterogeneous populations of both medical and surgical patients that may have influenced the incidence and outcome of organ failure. The purpose of this study is to establish the current incidence and mortality of organ failure in a homogenous population of critically ill trauma patients. METHODS All trauma patients admitted to the intensive care unit (ICU) at an urban Level I trauma center were prospectively studied. Patients were evaluated for the presence of organ failure using definitions proposed by Knaus and by Fry. Newer definitions of organ failure incorporating organ dysfunction and severity-of-illness scores were also obtained in all patients in an attempt to predict outcome. These included lung injury scores (acute respiratory distress syndrome scores), Acute Physiology and Chronic Health Evaluation (APACHE) II and III scores, Injury Severity Score (ISS), and multiple organ dysfunction scores. Primary outcomes assessed were death and the occurrence of organ failure by the various definitions. RESULTS Eight hundred sixty-nine trauma patients were admitted to the ICU and survived longer than 48 hours. Mean APACHE II and APACHE III scores at admission to the ICU and ISS were 12.2 +/- 22, 30.5 +/- 22.7, and 19 +/- 10, respectively. Single organ failure (SOF) occurred in 163 patients (18.7%) and multiple organ failure occurred in 44 patients (5.1%). All SOF was caused by respiratory failure. Respiratory failure occurred first in the majority of patients with multiple organ failure. Mortality was 4.3% with one organ system failure, 32% with two, 67% with three, and 90% when four organ systems failed. None of the patients with SOF died secondary to respiratory failure. Multiple stepwise regression analysis was performed to determine which of the following risk factors are associated with the occurrence of organ failure: mechanism of injury, lactate at 24 hours, ISS, APACHE II, APACHE III, acute respiratory distress syndrome score at admission, multiple organ dysfunction score at admission and total blood products transfused in 24 hours. Of these factors, APACHE III, lactate at 24 hours, and total blood products transfused in 24 hours were associated with the occurrence of organ failure. CONCLUSION The overall incidence of organ failure in a homogeneous trauma population appears to be lower than that reported in studies performed in heterogeneous patient populations in the 1980s. Mortality for SOF is low and appears to be related primarily to the patient's underlying injuries and not to organ failure. Mortality for two or three organ system failures is lower than reported 15 to 20 years ago. Mortality for patients with four or more organ system failures remains high, approaching 100%.