This study was undertaken to assess the factors influencing the postoperative range of motion after total knee arthroplasty (TKA). From January 1986 to December 1991, 111 TKA (Miller-Galante I System) surgeries were performed in 71 patients. Of those, 90 joints in 60 patients were kept under observation as the materials of this study. These patients included 37 patients with rheumatoid arthritis and 23 with osteoarthritis. The patients were divided into four groups according to postoperative range of motion (ROM), at the time averaging 51 months. The excellent group, defined as having more than 130 degrees range of motion consisted of 10 knees in 6 patients. The good group of 120 to 129 degrees had 19 knees in 13 patients; the fair group of 91 to 119 degrees consisted of 40 knees in 24 patients. In the poor group of 90 degrees or less there were 21 knees in 17 patients. Each group of patients was examined preoperatively, operatively, and postoperatively for factors relating to range of motion after TKA. The results of this study indicated factors influencing the ROM were: preoperative ROM, the primary indication, heights of postoperative joint line, patellar thickness, postoperative pain, and successive postoperative rehabilitation.