The Abdominal Trauma Index (ATI) was designed to stratify patients with penetrating injuries, and has been used to classify patients with blunt trauma. The Injury Severity Score (ISS) was originally designed to stratify victims of blunt trauma, and it has also been used for victims of penetrating trauma. We attempted to validate the use of ISS and ATI for both penetrating and blunt trauma. A total of 592 penetrating and 334 blunt trauma patients who underwent laparotomy over a 5-year period were evaluated. The overall rate of abdominal sepsis was 7.5% for blunt trauma and 7.6% for penetrating trauma. Mortality (excluding deaths within 48 hours) was 7% for blunt trauma and 1% for penetrating trauma. In the penetrating injury population, an ATI value greater than 15 and an ATI value greater than 25 were significantly associated with abdominal septic complications (ASCs) (p less than 0.001, both comparisons). An ISS greater than or equal to 16 was also associated with ASCs (p less than 0.001). The ASC rate for gunshots was higher than that for stab wounds (11% vs. 2%; p less than 0.001). In the blunt group, an ATI value greater than 15 and an ATI value greater than 25 were associated with ASCs (p less than 0.01 and p less than 0.001, respectively). The association of ASCs and ISS was linear with increasing ISS in patients with blunt abdominal trauma.(ABSTRACT TRUNCATED AT 250 WORDS)