[en] One of the difficulties associated with the application of CT for treatment planning of prostate cancer is the poor contrast between the apex of the prostate and the surrounding tissues. On MRI, these tissues are well differentiated, but due to the lack of geometric accuracy applications of MRI for treatment planning have been limited so far. We have previously developed an automatic 3D image correlation technique based on chamfer matching, which is routinely applied for head and neck patients. It is the purpose of this work to extend this technique for matching of pelvic CT and MR. Some of the problems encountered for this particular application are poor segmentation of the bone due to fat shift and geometric distortions in the MRI. However, a reasonable accurate match is obtained for the anatomy within the pelvis. The computation time is about 2 min for a full automatic correlation. However, due to the poor segmentation of the pelvic bones in MRI, the method sometimes fails and requires manual adjustment. Using matched CT and MRI, the position of the apex of the prostate could be easily determined and transferred to the CT scan for further treatment planning. It can be concluded that 3D image matching is a useful tool for treatment planning of the prostate