Twelve adult patients with pelvic sarcoma had implantation of a hemipelvic prosthesis. Eight patients had hemipelvic resection, and four patients had acetabulopubic resection. The implanted prosthesis was a special Vitallium prosthesis, which was specially designed for each patient with the aid of a computer. At a median followup of 57 months, eight patients were free of disease. In four patients with local relapse, two had additional resection, one had hindquarter amputation, and one was observed. In three patients with deep infection, the prosthesis was removed; however, one patient had hindquarter amputation. One patient had dislocation of the hip and prosthesis loosening. Overall survival of patients was 70%, and the survival of prostheses was 42%. In eight patients, the functional evaluation showed that the average functional score with the prosthesis was 11.6 (39%) and without the prosthesis the functional score was 7.0 (23%). Implantation of a megaprosthesis seems to indicate a high complication rate and a poor functional result after hemipelvic resection.