Large bone defects that occur after resection of calvarial tumours are commonly remedied using titanium meshes or bone prostheses. However, these methods have several problems. While intraoperative extracorporeal radiotherapy for bone flaps could avoid these problems, there have been only a few reports wherein meningiomas were treated with 120 Gy irradiation. Moreover, no reports are available on calvarial metastasis of sarcoma, and the therapeutic radiation dose remains uncertain. Here, we report a case of giant calvarial metastasis of myxoid liposarcoma treated with intraoperative extracorporeal radiotherapy at a dose of 50 Gy. The treatment resulted in successful tumour control followed by favourable bone reconstruction.