An analysis of the end results of ninety operations for fusion of an unstable knee due to anterior poliomyelitis is presented. The operation has been without risk and has resulted in no appreciable shortening of the leg. All but a small number of the patients were pleased with the end result. They were able to discard their braces and walk better. Eighty-five per cent. of them had good or excellent cosmetic and functional results. In the younger patients, thirteen years and less at the time of operation, postoperative deformity—flexion and knock-knee—is apt to occur. This is apparently due to gravity and unopposed action of the hamstrings on ununited epiphyses. Failure of fusion occurred in but two cases and was easily corrected by operative revision. The best results are obtained in those patients with paralysis limited to one leg, but the patients with both extremities involved are greatly benefited.