Sixty-one valgizing high tibial osteotomies performed according to the Insall method between 1975 and 1982 were reviewed; follow-up ranged from a minimum of 4 years to a maximum of 11, with an average of 7.5 years. The stage of preoperative osteoarthritis, evaluated according to Ahlbacks's classification, never exceeded Grade 3 (obliteration of the joint space and slight bone erosion). Preoperative varus never exceeded 10 degrees. The clinical results, evaluated on the score-form used at the Hospital for Special Surgery, were satisfactory in 48 cases (79% of the total) and unsatisfactory in 13 (21%). The success rate decreased to 65% in cases with a follow-up exceeding 10 years. There was frequently some loss of radiographic correction between the postoperative and follow-up values, but this was significant in only 9 cases where it exceeded 5 degrees. The arthritis was radiographically progressive in 22 cases, 18 of which were from the satisfactory group (excellent and good) and 4 from the unsatisfactory group (fair and poor). This positive evaluation of the results, even if they tended to deteriorate over a period of time, show that high valgizing tibial osteotomy is an effective operation, particularly when performed in knees without severe deformity.