The purpose of this study was to establish the optimal surgical treatment in patients with a Giant Cell Tumour (GCT) involving the acetabular bone. The surgical outcome in 10 patients with GCT involving the acetabular bone was reviewed. Patients were divided into two groups: group 1 in which 5 patients were primarily treated by curettage, and group 2, in which 5 patients were treated by resection and pelvic reconstruction. In group 1, local recurrence occurred in two cases. The functional outcome was excellent or good in 4, and poor in one case. There were no recurrences in group 2, in which the functional outcome was excellent or good in 4 and poor in one patient. The optimal surgical treatment modality should be based upon the tumour extension. Tumours located primarily in the ischiopubic region and not extending proximally beyond the supra-acetabular line can be adequately treated by extended curettage while those with further proximal extension are better treated by en-bloc resection. However, the possible complications of the different methods of pelvic reconstruction should always be considered.