OBJECTIVE The purpose of this study is to assess the diagnostic ability (sensitivity and specificity) of CT in the diagnosis of inflammatory abdominal aortic aneurysm (IAAA) and to quantitatively evaluate its features. METHODS A retrospective survey of 355 consecutive patients with abdominal aortic aneurysm and iliac artery aneurysm who underwent CT examination and surgical repair yielded 18 patients with operatively confirmed IAAA. The sensitivity, specificity, and diagnostic accuracy of CT were evaluated in this review. Eighteen IAAAs were then analyzed in terms of distribution and degree of perianeurysmal fibrosis as well as time-dependent change of CT values of the aneurysmal wall on contrast-enhanced CT. Complications related to IAAA were also determined. RESULTS Fifteen of the 18 cases of IAAA could be easily diagnosed on CT prior to surgical repair. Three false-negative and one false-positive case were found. This gives a sensitivity rate of 83.3% for this imaging technique, with specificity and accuracy rates of 99.7 and 93.7%, respectively. Thickening of the aortic wall was noticed mostly in the anterolateral wall of the aneurysm as compared with the posterior wall. The thickness of the perianeurysmal fibrosis correlated neither with the size of aneurysm nor with the inflammatory reaction such as erythrocyte sedimentation rate, C-reactive protein level, and white blood cell count. CT indicated the complications in 7 of 18 patients with IAAA. These included hydronephrosis, aortoenteric fistula, and infected iliac aneurysm. CONCLUSIONS CT scan with contrast enhancement was a highly reliable imaging modality for the diagnosis of IAAA.