AbstractThis paper describes the support system NUCSS (Nagoya University Craniofacial Surgical‐Planning System), which supports by computer the planning of craniofacial surgery using CT image. This is a total surgery planning‐assist system which plans the craniofacial surgery made traditionally by the surgeon by cutting and pasting pieces of paper on a two‐dimensional sketch of the skull image. Instead, the system displays the three‐dimensional image using computer graphics, and the planning is made interactively on the image. The major functions of the system are as follows. Generation and display of three‐dimensional image, three‐dimensional distance measurement on the skull, planning and execution of surgery on the side view of the skull, bone removal from arbitrary direction, and prediction of face after surgery. The features of the system are that the bone of arbitrary shape can be cut and shifted, and the face after surgery can roughly be predicted. This had been impossible in the traditi