Functional status expressed as Trauma Score (TS) and mechanism of injury were evaluated as criteria for diagnosing severe trauma in 253 traffic accident victims. An Injury Severity Score (ISS) of greater than or equal to 16 was considered a severe, potentially life-threatening injury. In 67 patients with ISS greater than or equal to 16, either TS was less than or equal to 13 or the history suggested risk of high energy trauma in 72%. When one or both of these criteria were met, ISS was greater than or equal to 16 in 54%. In addition, five patients (3%) with ISS less than 16 had potentially life-threatening injuries in the abdomen or in the thorax. Of these, two had a history indicating high energy trauma. Identifying severely injured patients by assessment of function and mechanism of injury gave an overtriage of 46%, which is acceptable, and an undertriage of 12%. Caution should be exercised in excluding severe trauma on these criteria. Considered together, decreased TS and a history indicating high energy injury, gave high sensitivity (72%) and specificity (78%) for diagnosing severe trauma, ISS greater than or equal to 16.