In case of aortic aneurysm, rapid surgery, such as stent grafting, was indispensable. Detecting aortic aneurysm manually is time consuming and imprecise. The objective of our study was to develop a fully automatic method for detecting and positioning the aortic aneurysm. A method was proposed to detect the presence of aneurysm in aortic model which was created from a set of multi-slice computed tomography (CT) images. A self-growing algorithm named Inner Sphere Growing (ISG) was also developed. The proposed method detected aneurysm as a region in which diameter of aorta increasing abnormally. The algorithm ISG successively obtained inner spheres along the aortic model, and gave the diameter information along the skeleton for the aneurysm detection. The validity of the method was confirmed by applying the method to a set of multi-slice CT images.In this paper, the principle and the procedure of the method were described. The application results were also shown.