Background: Cranioplasty is a well-known procedure, and autologous graft bone is usually considered the best choice in this procedure, but it cannot be used in conditions such as bone-infiltrating tumors, spheno-orbital en plaque meningiomas, and bone infections. Polymethylmethacrylate (PMMA) offers great possibility of intraoperative adaption. We describe a case of 1-step cranioplasty performed in a patient with a meningeal fibrosarcoma using a custom-made silicon mold., Case Description: A 48-year-old man was admitted to our department for a left temporo-parietal subcutaneous tumefaction that grew for a few months on the site of a previous osteodural decompression. After a biopsy that was diagnostic for meningeal fibrosarcoma, we planned tumor asportation, considering the bone infiltration of the tumor and the necessity of a cranioplasty. Before the intervention, we performed the craniotomy on a gypsum powder head phantom created based on a computed tomography scan. Then, using a computer-assisted design technique, a silicon mold was created and sterilized for the intervention. The edges of the preoperative simulated craniectomy were reproduced during the intervention using a rigid rail on the patient's scalp. The craniectomy was performed, and the tumor was removed. Then, a PMMA bone flap was made using a silicon mold and was fixed to the skull by miniscrews. Aesthetic results were considered excellent by the patient., Conclusions: We performed a 1-step cranioplasty after resection of a meningeal fibrosarcoma that infiltrated bone with a new technique to reproduce during intervention a preoperative simulated craniectomy and a computer-assisted design PMMA flap., (Copyright © 2017 Elsevier Inc. All rights reserved.)