In the department of Oral and Maxillofacial Surgery, Kiel, 120 individual skull models have been fabricated from 1986 to 1992. The purpose of this study is to compare the results of the 3-D-operation simulation with those of the operation planning based on clinical, radiological and cast analyses. 62 models, used for simulation of skeletal reconstructions, osteotomies and transplantation of bone, have been analysed. In 38 cases the previous operation planning could be proved by the model operation. 24 operation simulations, including secondary reconstructions of the midface and the mandible, asymmetric craniofacial anomalies and large transplants of bone, lead to more exact results as the planning without a model. We therefore regard these types of operations as good indications for 3-D-model operation planning.