Reconstruction of complex defects involving the maxilla or mandible often requires transfer of free vascularized tissue. In the conventional approach, a flap is transferred to provide vital tissue, and subsequent shaping and debulking are required. The authors present their experience with prefabrication of vascularized fibular flaps. Since 1999, 48 prefabricated flaps have been used to reconstruct 28 maxillary and 20 mandibular defects. The technique involves two surgical steps (prefabrication and flap transfer) and requires accurate planning, done with a solid model of the skull. Correct positioning of the prefabricated flap is accomplished by using the occlusion as a guide. Planning includes fabrication of a provisional prosthesis that is fixed to the flap with implants. Putting the prosthesis into occlusion determines the position of the flap.