We have verified our technical accuracy in a series of 72 high tibial osteotomies for medical gonarthrosis, which were operated following Install's technique. An acceptable alignment (6 degrees-15 degrees valgus) was achieved in 83% of the cases; a loss of correction during the healing phase was detected in 10% of the knees. We have modified some details of the previously employed technique in order to improve accuracy. The leg alignment is determined on 30 x 90 cm standing radiographs, defining the mechanical axes; we aim at 4 degrees of valgus. A guide is employed to determine the width of the wedge of bone to be removed. The osteotomy is fixed by means of two screws and wire; the fixation obtained is stable enough to allow early weigh bearing and range of motion. With these modifications we have been able to improve technical accuracy and we have rendered the postoperative course more acceptable to the patients.