60 patients undergoing high tibial osteotomy were randomized to undergo either lateral closing wedge or medial opening wedge high tibial osteotomy. The purpose of this study was to compare leg length changes and leg length discrepancies between these two methods, as well as to determine if there were any predictive factors related to the change in leg length with either technique. The results displayed that leg length discrepancy at 1 year postoperatively was significantly different in the medial opening wedge high tibial osteotomy group but was not significantly different in the lateral closing wedge group. Preoperative predictors for the change in leg length were found to be hip knee ankle angle in the lateral closing wedge group and change in tibial length in the medial opening wedge group.