Three-dimensional Computed Tomography (3-D CT) was performed in 21 patients for characterization of 29 aneurysms of various sizes and locations, and determining the relationship between the vascular and bony structures. These findings are compared with results ofaxial CT. digital subtraction angiography and operative observations. 3-D CT is a useful method for obtaining information about the detailed anatomy of cerebral vascular structures and aneurysms.