PURPOSE: The purpose of this study is to evaluate the CT and MR findings of brain absecss with emphasis on the thickeness and signal intensity of abscess wall. MATERIALS AND METHODS: Twenty CT scans and seven MR studies of 23 patients with brain abscess (27 abscesses) were retrospectively reviewed with respect to thickeness and signal intensity of abscess wall, shape and size of abscess, etc. Thickness of abscess wall was measured in the greatest abscess diameter on the CT scans and MR images obtaihed after intravenous administration of contrast material. RESULTS: Enhancing abscess wall was 2mm--6mm (average 3mm) thick. The abscess wall was uniform in thickness in 14 cases (52%), thinner in the roedial wall than lateral wall in 8 cases (30%), and thicker in the medial wall than lateral wall in 5 cases (18%). Signal intensity of abscess wall was isointense relative to gray matter on Tl-weighted MR images and hypointense on both proton- and T2-weighted MR images in 7 out of 8 lesione (88%). The inner margin of the abscess wall was smooth in 14 (52%) and irregular in 13 lesions (48%). The outer margin was smooth in 15 (55%) and irregular in 12 lesions (45%). The size of the abscesses was variable, ranging from lcm to 6cm in diameter. They were round (16 cases), elliptical (6 cases), or multilobulated (5 cases) in shape. Satellite or daughter abscesses were found in 5 patients. CONCLUSION: Abscess wall showed variable thickness in the medial and lateral walls with no specific findings. Other CT and MR findings were also nonspecific, although hypointensity of abscess wall on T2-weighted MR images may be helpful in diagnosis of brain abscess.