Between 1975 and 1986, cementless total knee replacement (Okayama University Mark-II or KC-1) was performed on 38 osteoarthritic knees of 30 patients over 65 years old. Five patients died of unrelated causes from 3 to 6 years after the surgery. A follow up study was carried out for over 3 years in 27 knees of 20 patients. The mean length of follow-up was 69 months, ranging from 36 to 116 months. The average clinical knee score by three university knee score system was 37.1 points preoperatively and improved up to 77.6 points at the follow up. Pain relief was clinically excellent and correction of the deformity was also sufficient. Clinical and radiographic evaluations were also made in correlation with osteoporosis of the knee. According to Foltin's classification of osteoporosis of the knee, operated knees were grouped into five grades (IV), and about 80 percent of the patients had osteoporosis of more than grade III. Radiographically, loosening or migration was observed in 5 knees (19%) in this series, and all of the patients had severe osteoporosis. In other patients with osteoporosis, the clinical knee score improved similarly, but in about half of them there was some change in the femorotibial angle or medial or posterior angle of the tibial component. Therefore, such changes should be followed in radiological examinations in relation to the clinical course.