In thoracoscopic surgery for mediastinal or chest wall lesions the suitable position of ports( trocars) are required depending on the position of a target lesion in a particular patient. We have therefore developed a virtual reality (VR) simulation system using the specific data of each individual patient. The model data generation system, PASS-GEN, is customized for thoracic surgery. The chest wall and organs around the tumor are extracted from DICOM image data of computed tomography (CT) scan, and three-dimensional (3D) virtual images are constructed. Rehearsal of ports insertion is carried out by locating the scope and the forceps anywhere on the chest wall on PC monitor. The constructed VR images clearly show three dimensional relationships between the target and surrounding structures. This system also simulates circumstances where on the chest wall a thoracoscope and tools should be inserted for the better view and more comfortable manipulation. Particularly in mediastinal or chest wall surgery VR simulation is more practical because those structures would be less transformed during operation.