Our aim was to evaluate the alteration in angle of posterior slope of the tibia and the degree of patellar height following medial opening wedge high tibia osteotomy(HTO) using autologous tricortical iliac bone graft in 32 consecutive patients. Twenty three females and nine males underwent medial opening wedge high tibia osteotomy (HTO) using autologous tricortical iliac bone graft in 34 knees (33 primary medial compartment osteoarthritis and 1 idiopathic osteonecrosis of medial tibial condyle). The posterior slope of tibia was determined by the proximal tibial anatomical axis. Patellar height was measured by the Insall-Salvati and the Blackburne-Peel ratios. Preoperative and postoperative (last follow up) values of these three parameters were compared. The intra- and interobserver variability of these methods was determined before and after operation. At the end of mean follow up of 3 years this procedure produced no significant change in posterior slope. Pre and postoperative posterior slope were 8.7 degrees+/-3.6 degrees and 8.2 degrees+/-2.8 degrees respectively (P=0.412). Pre and postoperative Insall-Salvati ratios were 0.93+/-0.10 and 1.05+/-0.11 respectively (P<0.001). The Insall-Salvati ratio increased in 94% of patients and patellar ligament length was significantly increased. The distance between the patellar and tibiofemoral joint line decreased in 82% of patients. The mean Blackburne-Peel ratio declined from 0.71+/-0.12 to 0.61+/-0.13 (P<0.001). Twenty six percent of postoperative Blackburne-Peel values satisfied the radiographic criterion for patellar infera (Blackburne-Peel ratio<0.54). There was no difference in the intra-and interobserver variability of measurements either before or after HTO. Opening wedge HTO using autologous tricortical iliac bone graft with internal fixation and early mobilisation prevented change in posterior slope of tibia, lengthened the patellar ligament and elevated the tibiofemoral joint line when the mean ratio of anterior and posterior gap at the osteotomy site was around two-thirds.