In this chapter effects of a cranial defect and methods of cranioplasty are discussed. Cranial defects result from trauma, decompressive craniectomy, infection and neoplasms. Motor vehicle accidents, industrial accidents and gunshot wounds are the most frequent causes. Treatment of depressed skull fractures and wounds produced by penetrating missiles frequently result in skull defects. Indications for cranioplasty are cerebral protection and cosmetic repair; syndrome of the sinking skin flap and “syndrome of the trephined”. Titanium and PMMA are the widely used synthetic graft. In growing children autogenic bone grafts must be used. It is better to use minimal amount of nonmagnetic and radiolucent foreign material to achieve fixation. Tissue engineering holds great promise for the future treatment of osseous defects.