Eighty-three Waildius arthroplasties, performed by one surgeon as a salvage operation on the knee joint between 1966 and 1972, were independently reviewed. The fifty-seven living patients with sixty-seven arthroplasties were interviewed and examined and the clinical records of the deceased patients were inspected. Sixty-seven arthroplasties (81 per cent) were successful and sixteen failed (19 per cent). Acrylic cement was used to secure the prosthesis on eight occasions only. There were two primary infections (24 per cent) and two delayed (24 per cent). Major loosening occurred in three arthroplasties (36 per cent). Minor loosening was compatible with a good result. Arthrodesis was successful on the two occasions on which it became necessary to remove the implant. There were no disasters. On the basis of these results it is considered that the Walidius arthroplasty can justifiably be offered as an alternative to primary arthrodesis of the knee.