Seventy patients who had a rotationplasty for treatment of a malignant tumor in the region of the knee (the femur or the tibia) between 1974 and 1987 were followed for two to thirteen years (mean duration of follow-up, four years). Forty-seven patients had a stage-IIB osteosarcoma; the remaining twenty-three patients had a malignant fibrous histiocytoma, a chondrosarcoma, a Ewing sarcoma, or a giant-cell tumor. The most severe postoperative complication was occlusion of the reanastomosed vessels (seven patients), leading to amputation proximal to the knee in three patients. Other complications were problems with wound-healing (eight patients), transient nerve palsy (five patients), irreversible nerve palsy (two patients), pseudarthrosis (four patients), and rotational malalignment (one patient). Late complications included eight fractures, two infections, two delayed unions, and one lymphatic fistula. More than half of the patients were free of complications related to the operative procedure. Forty-four of the patients who had a stage-IIB osteosarcoma could be followed, and their data were analyzed for survival statistics. These patients had a 58 percent rate of disease-free survival and a 70 per cent rate of over-all survival. One patient had a local recurrence five years after the operation.