PURPOSE: The purpose of this study was to assess the relative diagnostic capability of magnetic resonance angiography(MRA) and CT angiography(CTA) in the evaluation of intracranial aneurysm. MATERIALS AND METHODS: MRA and CTA were performed in 14 intracranial aneurysms (Including four which were ruptured) confirmed in the II patients involved by conventional angiography(CA). The size(in largest dimension) of the aneurysms ranged between 3 mm and 20 mm and the mean was 10.5 mm. For MRA, the 3D TOF method, with magnetization transfer suppression, wasused at 1.5T. For CTA, twenty seconds after beginning the injection of contrast media(100mL with use of a power injector at the rate of 3 mL/sec), CT scanning(30-second exposure and 60-mm length) was performed with a table speed of 2 mm/sec and a section thickness of 2mm. The resulting data were reformatted by MIP. MRA and CTA were compared with regard to the detection of aneurysms and their neck, size, shape, direction, intensity and relationship to adjacent bony structures or vessels. RESULTS: All aneurysms were clearly visualized with CTA. Inone case with a 3-mm aneurysm, however, this was not defined on MRA. Of the 13 aneurysms demonstrated by both MRA and CTA, eight were seen equally well with both modalities. CTA was considered to be superior to MRA in fivecases, either because calcification in the aneurysm wall was seen only on CTA(n = 3) or because the relationship with adjacent bony structures were seen better with CTA(n = 2). With CTA, the intensities of the aneurysm were homogeneous in all cases ; with MRA, however, the intensities of three large aneurysms were different. CONCLUSION: MRA and CTA may be useful in the evaluation of intracranial aneurysm, CTA has specific advantages over MRA inthe evaluation of large aneurysms, calcification of aneurysm wall and relationship with adjacent bony structure.