Aneurysmal bone cyst (ABC) is a relatively rare, non-neoplastic expansile lesion of bone. Bleeding may occur during an operation or biopsy for ABC, as this cyst is an aneurys with numerous pools of blood. Therefore, it is necessary to diagnose ABC before treatment or biopsy. In the present report, we describe the characteristic computed tomography (CT) and magnetic resonance imaging (MRI) features of ABC in the mandible. Based on the literature and on our own experiences, we compare with the features of ABC with the corresponding features of other lesions showing similar conventional radiographic appearances. In the present case, bone-targeting CT showed the characteristic feature, which reflected the histopathological appearance of a partially cystic meshwork divided by coarse septa. MRI showed almost homogeneous intermediate signal intensity, including a partial slight low-signal-intensity area on the T1-weighted image, and homogeneous high signal intensity, which showed a 'bubbly' appearance, on T2-weighted image. On the enhanced T1-weighted image, the intermediate signal intensity areas apart from the areas that showed slight low-signal intensity on the non-enhanced T1-weighted image, were well enhanced. This creates a 'honeycomb' appearance. The 'meshwork' appearance on bone-targeting CT, the 'bubbly' appearance on the T2W1 and the 'honeycomb' appearance on Gd-T1WI may be the characteristic features of ABC. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.