Severity of injury, patient age and preexisting medical conditions, time from injury to treatment, and quality of care rendered are generally recognized as major determinants of outcome after trauma. In a retrospective review, we compared 456 elderly patients (age greater than or equal to 65 years) with traumatic injuries to 985 younger patients (age less than 65). We compared cause of injury, injury severity score (ISS), seven risk factors indicating preexisting disease, complications, length of stay, and mortality. Overall mortality was 6.0% for patients aged less than 65 years and 8.6% for those older than 65. The injury severity score at which the probability of death was 10% was 17.3 in the older group and 24.9 in the younger group. Factors associated with outcome included cause of trauma (P less than .001), ISS (P less than .001), and number of complication factors (P less than .01). Preexisting risk factors were not significantly associated with outcome. We conclude that trauma in the elderly causes higher mortality with less severe injury, and that the mortality is related to the cause and severity of the trauma and the number of complications, and not to pre-existing disease. Length of stay increases with the severity of injury, except in the severely injured, who die.