The importance of a preoperative bone scan before tibial osteotomy is to detect the extent of specific compartmental involvement of the osteoarthritic knee. It is not necessary to obtain a bone scan in every case, but when difficulty arises in the selection of patients for surgery, whether the opposite compartment is involved by disease or not, a preoperative bone scan becomes useful and may eliminate the need for other procedures such as arthroscopy and arthrotomy. In a series of cases of osteotomy in 21 knees of 22 patients, with an average follow-up of 15 months, all had a preoperative bone scan, 14 repeated postoperatively. Satisfactory functional results were obtained in 71%.