We report the case of a 20-month-old boy with autologous bone graft resorption that resulted in a floating bone graft and progressive asymmetric deformity of the skull. The patient had undergone decompressive craniectomy for acute subdural hematoma at the age of 13 months after a fall, followed by cranioplasty 1 month later with an autologous bone graft , which was stored in a freezer immediately after surgery. We used the mortise and tenon principle to replace the screws and plates to join a polymethylmethacrylate prosthesis to the skull, augmenting the resorbed autologous bone graft. The cosmetic effect was maintained and craniocerebral protection was restored. It is thought that his technique could be used for bone defects of various sizes in patients of any age in cases where screws and plates are not suitable. ; 附設醫院雲林分院 ; 醫學院附設醫院 ; 期刊論文