PURPOSE: To classify the cavernous sinus lesions, to describe their radiological findings, and to assess the usefulness of MR compared to CT. METHODS AND MATERIALS: Fourty-five patients with lesions involving the cavernous sinus proved by histological and/or clinical and imaging methods were studied retrospectively and classified into neoplastic, vascular, and inflammatory lesions. CT and MR findings were compared in 21 patients evaluated by both modalities simultaneously according to these 4 categories. RESULTS: Pitiutary macroadenoma was the most common cavernous sinus lesion(42%). Diffuse convex bulging of the lateral wall of cavernous sinus was the most frequent radiological finding(84%), and the others were encasement of the cavernous carotid artery(49%), remodelling of the surrounding bones(44%), and complete obliteration of Meckel's cave(38%), in descending order of frequency. Bulging of the lateral wall of cavernous sinus was equally well demonstrated on both modalities, but encasement or displacement of the cavernous carotid artery and complete or partial obliteration of Meckel's cave were much better delineated on MR than on CT with the ratio of 3.8:1 and 4.6: 1, respectively. Only bone changes were much better demonstrated on CTthan on MR with the ratio of 3.8: 1. CONCLUSION: MR issuperior to CTin demonstrating thecavernouscarotid artery encasement and obliteration of Meckel's cave, but CT is much better than MR in demonstrating bone changes.