Stoma site marking is performed by inspection and palpation of the body surface. In stoma site, it is estimated that transverse colon is epigastric lesion and sigmoid colon is left hypogastric lesion. We try making colostomy simulation(Cs)3D-CT by which stoma site marking is able to be performed considering exact form of colon.The patient was 50s man with advanced rectal cancer and unresectable multiple liver metastases. Colonostomy was scheduled for strong rectal stenosis. Standard contrast-enhanced CT scan was performed before operation, and 3D-CT imaging was maked using Workstation Ziostation2(ziosoft, Tokyo, Japan). 3D-CT imaging of abdominal wall was maked by synthesizing 3D-CT imaging of body surface and rectus abdominis muscle. Cs3D-CT is maked by synthesizing CT colonography and 3D-CT imaging of abdominal wall.The simulation of stoma site marking was performed using Cs3D-CT. Inferior epigastric artery(IEA)was identified, it was to simulate elevated colons and the stoma sites to enable easy elevation of colon through rectus abdominis muscle avoiding injury of IEA. It was possible to measure the distance from navel to stoma site marking on 3D-CT imaging, final stoma site marking was decided by applying the simulation to real stoma site marking. The difficulty of operation was assessed from positional relationship between colon and abdominal wall. It seemed to be relatively easy to elevate sigmoid colon because sigmoid colon was directly under the rectus abdominis muscle. Sigmoidostomy was scheduled considering rectal cancer, and trephine sigmoidostomy with double orifices was performed in fact.Cs3D-CT was possible to simulate colostomy considering the exact form of colon and positional relationship to abdominal wall and to perform stoma site marking considering the exact form of rectus abdominis muscle and position of IEA. Using Cs3D-CT, it seems to be able to perform optimal stoma site marking which is difficult by conventional method.