Recently there has been decreasing trend of high tibial osteotomy in management of the gonarthrotic patients partly due to recurrence of the symptom and, more importantly, due to the relative success of the total knee joint replacement procedure. But there is still room for the high tibial osteotomy, although it may be 'outdated' procedure, in that younger active patients do well postopera- tively for an enough period of time and that even the older have some gain of pain-relief in early postoperative period. The purpose of this study is to detect the affecting factors of the result of the operation. We reviewed 25 valgus high tibial osteotomies in 23 patients who had medial gonarthrosis and could be followed-up more than 1 year among 32 cases between August 1989 and January 1994. The mean length of follow-up was 30 months(ranged twelve to fifty four months). The results were compared according to modified grading of the HSS score. All cases showed the increase of the score from preop. average 65.2 points to postop. 87.8 points, mainly by the decrease of pain and the increase of functional activity. The severity of degenerative change on the radiographs and the degree of varus seemed to be related with the early clinical results of the operation, but the age was not a major affecting factor. These results could be debatable due to some differences from the others', and long term follow-up would be needed.