Partial replacement of the pelvis by special prosthesis after resection for malignant lesions becomes more and more a rewarding alternative to the mutilating amputive procedures. A new method is recommended facilitating the forming of suitable prostheses. With computerized axial tomography it is possible to construct an actual sized three-dimensional model of the patients pelvis. This model is a very useful aid in preparing the special prosthesis as it corresponds exactly with the anatomic shape of the resected part.