Diverse therapeutic modalities have been proposed to treat the minimal or moderate degree of osteoarthritis of the knee joint. Conventional arthrotomy and debridement with such complications as stiffness and instability were a popular procedure before the advent of high tibial osteotomy and arthroscopy. Coventrys proximal tibial osteotomy has been an appealing method for the treatment of degenerative osteoarthritis with varus angular deformity. Coventry himself, however, mentioned that arthrotomy might aggravate the knee stiffness when combined with his procedure. Recurrence of deformity and pain has been popular complications because of the residual pathology inside the joint. The first group of 12 knees from 10 patients treated by proximal tibial osteotomy only was compared with the second group of 17 knees from 13 patients treated by combination of arthroscopic debridement and proximal tibial osteotomy. The operations had been performed between March 1985 and September 1989. The result is as below; 1. The average follow-up period of the first group was 24.5 months versus 12.3 months in the second group. 2. The preoperative varus angle and valgus correction at the final follow-up of the first group were 9.0°and 6.4°versus 8.9°and 7.8°in the second group. 3. Change of Insall's Knee score between preoperative and final follow-up periods in the first group was 58.2 and 81.5 versus 55.3 and 86.4 in the second group. 4. A combination of arthroscopic debridement and proximal tibial osteotomy could be an appealing alternative to total knee arthroplasty in selected cases.