The authors have treated three patients with extensive involvement of the acetabular and periacetabular bone by a malignant tumour. One had a metastasis from a carcinoma of the thyroid, one from a carcinoma of the breast and one a plasmocytoma. In all three cases, the upper part of the femur was unaffected. It was used to replace the resected innominate bone and fixed to the remaining bone by screws and plates. An acetabular cup was cemented into the transplanted bone, which itself was replaced by a massive femoral prosthesis. This technique allowed the patients to resume weight bearing rapidly. Two patients were alive and walked satisfactorily after two and four years respectively. The third died five months after the surgical procedure.