The first fifty kinematic rotating-hinge total knee arthroplasties that were done at the Mayo Clinic were reviewed. The indication for use of this prosthesis was either ligamentous instability or loss of bone, or both. At a mean length of follow-up of fifty months (range, twenty-nine to seventy-nine months), the clinical results of thirty-eight knees in thirty-six patients were evaluated. Fifteen of the thirty-eight knees had had a primary arthroplasty and twenty-three had had a revision arthroplasty using the kinematic rotating-hinge prosthesis. Using the knee-rating score of The Hospital for Special Surgery, there were fourteen excellent, twelve good, five fair, and five poor results. For two knees there was inadequate information to calculate a knee-rating score. Lucent lines that were more than one millimeter in width were seen with 25 per cent of the femoral and 50 per cent of the tibial components. Progression of lucent lines was observed in thirteen knees, and five knees showed probable radiographic loosening. The high incidence of complications was distressing, with a 16 per cent rate of sepsis, a 22 per cent rate of patellar instability, and a 6 per cent rate of breakage of the implant. In our opinion, this implant should be used only in knees in which there is functional absence of a collateral ligament that cannot be managed by soft-tissue reconstruction.