OBJECTIVES. The aim of this study was to assess the effectiveness of corrective high tibial osteotomy in the treatment of degenerative knee arthritis. Success is defined by increased mobility, reduced pain intensity and physiological angle correction after surgery. STUDY DESIGN. Retrospective-prospective study. PARTICIPANS AND METHODS. The study included 19 patients treated at the Institute of Orthopaedic Surgery, University Hospital Center Osijek who underwent corrective high tibial osteotomy from 2005 to 2015 because of the degenerative arthritis of the knee joint of the 2nd and 3rd degree of deviation from the axis of the knee joint. The data was obtained from existing medical records (medical history, local status and radiography). The degree of arthrosis is determined by the Kellgren - Lawrence classification. RESULTS. After the operation of the knee arthrosis by corrective osteotomy of the tibia, there was an increase range of motion in the knee joint (Wilcoxon rank-sum test, median before surgery, 110°; the median after surgery, 120°), the sensation of pain, defined by VAS scale from 1 to 10, was reduced (Wilcoxon rank-sum test, median, 8 before surgery; after surgery median, 3), and femoro-tibial angle reduced (Wilcoxon rank-sum test, median 184° before surgery, after surgery median 178°). CONCLUSION. Treating knee arthrosis by the corrective tibial osteotomy is a successful method because it leads to an increase in range of motion of the affected knee and a significant reduction of pain sensation and reduces femoral-tibial angle.