Ninety-eight cases of surgically proved bowel perforation in VGH-Kaohsiung within one year were reviewed. Among them, 25 patients received abdominal CT scans before operation. Free gas or fluid could be demonstrated with CT scan in 80% of cases though sometimes the fluid was too scanty to be well recognized. Local abscess formation with or without tumor mass lesion (n = 3), local fluid accumulation (n = 1) and negative CT findings (n = 1) constituted the remaining 20% of cases. The recognition of perforation sites depended on direct evidences of perforation such as ulceration, abscess formation and tumor mass lesion (32%), or indirect evidences including hematoma formation, dependent extraluminal gas accumulation and phlegmonous reaction (12%). An inexplicable localized extraluminal fluid accumulation might also suggest a possibility of hollow organ perforation and lead to the recognition of perforation site in the absence of free gas (4%). Absence of extraluminal fluid or gas can not completely rule out the possibility of hollow organ perforation (4%). Massive free air, especially with an air-fluid level, suggested a possibility of upper abdominal perforation. The perforation hole located at the anterior wall of stomach produced more free gas than that located at posterior wall. Air-fluid levels could never be identified in the cases of lower gastrointestinal perforations. Local bowel wall thickening and the distribution of free gas contributed little to the recognition of perforation site. Extravasation of oral contrast media sometimes led to the diagnosis of gastrointestinal perforation but was not necessary to be noted around the perforation hole and did little contribution to the perforation site recognition.(ABSTRACT TRUNCATED AT 250 WORDS)