The results of unicompartmental knee arthroplasty are still controversial. The purpose of this study is to evaluate the clinical results of three different component systems of unicompartmental knee arthroplasties. From December 1982 to January 1996, 106 unicompartmental knee arthroplasties were performed. There were 13 Modular II(group I), 47 Microloc(group II) and 46 Allegretto(group III) unicompartmental knee arthroplasties. Average follow-up period was 7 years 1 month. At the last follow-up, average knee score of Hospital for Special Surgery(HSS) was 92 points and average tibiofemoral angle was valgus 3.5 degrees. Among three groups, there was no significant difference in knee score of HSS and tibiofemoral angle. Twelve knees(11%) in all three groups have required revision. The causes of revision were six implant wears(all in group II), five implant loosenings(one in group I and four in group III) and one deep infection(in group II). In conclusion, the results of unicompartmental knee arthroplasty at average 7.1 years follow-up period were satisfactory. High incidence of insert wear in Microloc unicompartmental knee arthroplasty(group II) might be due to thin polyethylene insert supported by metal backed tibial tray.