One of the most serious problems in medical science is an increment of Alzheimer's disease. It is known that the patient's brain atrophy is a result of neural cell loss. It is useful for the diagnosis of Alzheimer's disease to measure the volumes of the brain portions and to display them. We can obtain anatomical information from 2D slice images produced by MRI. We propose a computer-aided system for the diagnosis of Alzheimer's disease. The system consists of: (1) extraction of the portions from MRI data, (2) measurement of the volumes of the portions and then displaying them, and (3) user interface for a medical doctor. In this paper we describe procedures for the above. For extraction of the brain portions we propose the method based on standard region growing algorithm and the method of figure decomposition using the distance value. Comparison of the volumes of our extracted portions with volumes manually measured by a physician shows that the error rate, on the average, is 1.74% for 48 MRI data. We also discuss the 3D display, the measuring range, and the construction of the user interface for a physician. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(4): 32–41, 1997