PURPOSE: To evaluate the CT findings which may help differentiate pelvic inflammatory bowel mass(IBM) fromtubo-ovarian abscess(TOA). MATERIALS AND METHODS: Twenty-five patients with histologically confirmed TOA(n=14),periappendiceal abscess(n=9), an abscess caused by diverticulitis(n=1), and by ulcerative colitis(n=1) wereevaluated. For TOA, age distribution ranged only from the 3rd to the 5th decade, but for IBM, the range was the 2nd to 8th decade with highest frequency during the 3rd-4th decade. CT findings were retrospectively analysed forbilaterality, internal septa, anterior displacement of the mesosalpinx, and perirectal and mesenteric fat. RESULTS: Mesenteric fat infiltration was detected in all 11 cases of pelvic IBM, but in only two of 14 TOA cases(p<0.05).Anterior displacement of the mesosalpinx was observed in two of 11 pelvic IBM cases and in nine of 14 TOAcases(P<0.05). There were no significant difference in bilaterality, internal septa, or perirectal fatinfiltration. CONCLUSION: Mesenteric fat infiltration was the most reliable finding in differentiating pelvic IBMform TOA. Anterior displacement of the mesosalpinx, and age distribution were also helpful in differentiating thetwo disease groups.