The use of seatbelts has reduced the overall mortality associated with motor vehicle accidents. The use of lap belts has, however, been associated with a constellation of abdominal injuries, which has been termed "the seatbelt syndrome." Previous studies have shown no increase in overall rates of abdominal injury but an increase in intestinal injury with the use of lap belts. Retrospective reviews suggest that the presence of a "seatbelt sign" may further increase the risk of intestinal injury. The purpose of this study is to prospectively evaluate the incidence of abdominal and intestinal injuries in patients with a "seatbelt sign." A consecutive sample of 117 adult motor vehicle accident victims were studied between July 1993 and January 1994. The use of seatbelts and the presence or absence of a seatbelt sign were determined on admission. Patients were evaluated with computed tomography scan of the abdomen, diagnostic peritoneal lavage, serial abdominal examinations, and operative findings. On arrival, 14 of 117 (12%) had an abdominal seatbelt sign. Of these 14, 9 (64%) had abdominal injury, 5 (36%) required operative intervention, and 3 (21%) had small bowel perforation. In contrast, the 103 patients without a seatbelt sign had significantly fewer abdominal injuries (9; 8.7%), laparotomies (4; 3.8%), and small intestine perforations (2; 103; 1.9%). We conclude that the presence of a seatbelt sign is associated with an increased likelihood of abdominal and intestinal injuries and mandates a heightened index of suspicion.