A prospective follow-up using a standardized data recording form was carried out by independent, experienced orthopedic surgeons on a small number (116) of knees operated upon at The London Hospital in the period January 1, 1971 to October 31, 1973. An additional 93 knees have been operated upon at other hospitals and followed prospectively using the same data recording system. A total of 159 knees have been reviewed 2 to 4 years after operation. The complications specific to ICLH arthroplasty have been unremarkable and generally correctable. Two tibial components have sunk and have been revised at The London Hospital. The results show that ICLH arthroplasty has been used to correct satisfactorily flexion deformities up to 70 degrees, valgus deformities up to 45 degrees, and varus deformities up to 35 degrees. (Deformities of greater magnitude can be corrected but were not present among the knees in this study.) The operation may be said to be "worthwhile" with reference to pain in 94 per cent of the knees, with reference to the ability to walk in 80 per cent of the knees, and with reference to the range of movement in 71 per cent. Overall, 47 per cent of the knees had no complaint postoperatively, while a further 47 per cent were improved; thus for 94 per cent the procedure was "worthwhile."