In 1975, the Okayama Mark Ⅱ prosthesis was introduced at the Okayama University Hospital and 21 patients (33 knees) with rheumatoid arthritis were followed for ten years or more after implantation of the device. The average follow-up period was 13 years and 7 months (range, 10 years and 3 months to 16 years and 4 months). The average age at surgery was 50 years and 4 months. There were 3 male patients. Clinical results were assessed using a knee assessment chart designed by three universities. Femorotibial angle and the setting angle of the tibial and femoral components in relation to the axes of the tibia or femur were examined on X-rays. Clinical assessment improved from 39.8±15.7 points to 71.2±18.3 points (five-year follow-up), and decreased to 62.2±17.9 points at final examination. On X-ray, the alpha angle (one of the setting angles of the tibial plate) decreased from 88.0±3.0 degrees (at postoperative examination) to 86.7±3.7 degrees (at final examination). Also on X-ray, femoral components appeared to sink proximally in 36% of our cases. There were few problems with tibial components of the Okayama Mark Ⅱ prosthesis despite the lack of a metal-backed tray on the tibial component. The sinking of the femoral component occurred relatively more frequently with the Okayama Mark Ⅱ than with other types of total knee replacement.