We reviewed retrospectively the results in patients who had undergone one hundred and four high tibial lateral osteotomies. The operations were all performed between 1985 and 1993. Each one of fifty men and forty nine women demonstrated a varus deformity of the knee with a coexistent medial osteoarthritis. Results were reviewed in 49 patients (62 knees) with an average follow-up of 10.2 years (range 6-14 years). Of the remaining 42 patients, 8 were lost to follow-up, 10 had died, and 24 were subsequently treated with total knee arthroplasty at an average 4.7 years after having had a high tibial osteotomy. Clinical results were evaluated using the Hospital for Special Surgery Score (HSS) and the Knee Society Score. Radiographs were systematically analysed to evaluate osteoarthritis and leg axis. Forty four (90 per cent) of the forty nine patients stated the results met their expectations and given the same circumstances, they would have the operation once again. In these patients the knee score results were excellent. The same patients had excellent HSS and Knee Society Scores. Five patients (10 per cent) had a poor result and twenty four patients were treated later by total knee arthroplasty because of pain. The following factors set these patients apart from those with more favorable results: previous arthroscopic debridement, obesity, lateral knee osteoarthritis, insufficient valgus correction, and an age of more than 55 years. High tibial valgus osteotomy provides good pain relief and improved function in carefully selected patients. Our results support this conclusion.