We treated four patients with periacetabular malignant tumours by pelvic reconstruction with a free vascularised fibular graft after resection of the tumour. The mean follow-up period was 32 months (9 to 39). The diagnosis was chondrosarcoma in three patients and osteosarcoma in one. In two patients total resection of the hemipelvis was required and in the other two less, but still massive, resection was undertaken. All were treated with an immediate free vascularised fibular graft which included arthrodesis of the hip and reconstruction of the pelvic ring. One patient died. The other three have remained free from recurrence. Solid union of the graft was achieved between four and 14 months after surgery. Shortening of the involved limbs was less than 2 cm. The patients had no pain and were independent walkers without external support. Emotional acceptance was satisfactory. Our results suggest that reconstruction with the use of a free vascularised graft is an alternative to other types of reconstructive procedure after resection of periacetabular tumours.