A new method for elucidating the process of abdominal aortic aneurysm enlargement is presented herein. First, 3-dimensional (3-D) reconstructed images were used to precisely evaluate the size of an aneurysm, after which reconstruction and a volume analysis of images were performed with a personal computer system using serial computed tomographic films. The evolution of an aneurysm was examined by the detailed reconstruction, and an estimation of size was achieved by accurately measuring the figure reconstructed from the angle perpendicular to the axis of the contour. In quantifying the enlargement of an aneurysm, an exact evaluation of volume changes and morphological changes can be performed using the 3-D reconstruction method from the film series obtained at follow-up studies. The volume analysis proved especially useful for evaluating the axial expansion of aneurysms with stable maximum diameters.