Simulation of the needle puncture and volume estimation for the tumors in the liver were carried out with the three-dimensional image reconstruction system, which consists of a medical image acquisition system, a data processing system, and a graphic display. A set of sliced-image data from a computerized tomography and/or a magnetic resonance imaging was used to reconstruct the liver, the vessels, and the tumors of the patients with liver cancer. A good agreement of anatomic locations of both the intrahepatic vessels and the tumors between the reconstructed liver model and the echography done intraoperatively was observed. Surgical simulations with these graphic models clearly indicated safety areas for needle puncture in the laser coagulation therapy. In addition liver volumes were calculated within 3% of error in comparison to the measured values. These results indicate that the computer-aided surgery system is a highly promising method that avoids cumbersome stereoscopic recognition of the anatomical location of the diseased area and the vessels, before and after surgery.