In the lateral roentgenographic cephalometric analysis, a certain degree of errors is unavoidable as it involves a lot of manual work in tracing, landmark setting, measurement and registration. To minimize the chances of errors creeping in, efforts have been made toward the mechanization of manual work. For measuring and registering automatically, a roentgenographic cephalometric system using a personal computer is available. Attempts have also been made to automatically obtain landmarks on tracings by the use of a computer. However, tracing still has to be performed by hand. The circumstances are such that the development of a full-scale scanning system that can perform automatic tracing on cephalometric radiographs in being eagerly awaited. The present study concerns the possibility of using a small-size computer mainframe in a small-scale clinical laboratory which cannot afford to install a large one. A digital image processing system using a personal computer was devised to process cephalograms. And a the anatomical complex on the screen was developed. To examine the acuracy of the drawings, comparisons were made between manual tracings and computer-aided tracings. The results were as follows: 1. In both vertical and horizontal components at Pog, Gn and Me points, computer tracings were matched significantly well with manual tracings. 2. At the points of Or, ANS, A and Go, only vertical components were matched significantly well with those obtained by manual tracing. 3. In the program developed for the present study, the computer had a greater tendency than man to draw the borderline along the higher density area when the gray level gradient was not sharp.