PURPOSE: The high mortality and morbidity rates associated with traumatic rupture of the small bowel have been attributed to the clinical difficulty of establishing an early diagnosis. CT scan is the most widely used tool for the diagnosis of blunt abdominal trauma, but its accuracy in diagnosing small bowel perforation is still controversial. This study was conducted to determine the overall and time-dependent diagnostic value of abdominal CT and the clinical findings of small bowel perforation. METHODS: The clinical data and CT images of 21 patients with small bowel perforation after blunt trauma were retrospectively analyzed. The patients were divided into the early and late elapsed time groups based on the elapsed time of 8 hours from the initial trauma to the time of evaluation. RESULTS: Any changes of the vital signs, including hypotension, tachycardia or fever, were observed in only half of the patients. Signs of peritonitis were evident in 7/11 of the early lapse group and in 10/10 of the late lapse group. The most common CT finding of small bowel perforation was free peritoneal air (17 of 21 patients), followed by segmental bowel wall thickening (15/21), high density ascites (14/21), an intermesentric fluid collection (13/21) and mesentic fat obliteration (11/21). Extraluminal air and segmental bowel wall thickening were detected more frequently in the late lapse group (P=0.03 and 0.01, respectively). In the one patient, bowel perforation was not evident at the initial evaluation according to the clinical findings and CT, but the follow-up CT exam showed specific findings for bowel perforation. CONCLUSION: CT scanning is a sensitive and effective modality for the evaluation of small bowel perforation, but this is less sensitive during the earlier post traumatic period. Therefore, careful clinical and radiological follow up is necessary for suspected cases, and even when an initial evaluation shows negative findings for bowel injury.