OBJECTIVE: To study the long-term outcome of surgical removal of a meniscus in the knee with regard to radiographic signs of osteoarthritis (OA). METHODS: Of the 123 patients who underwent an open meniscectomy due to an isolated meniscus tear in 1973 at Lund University Hospital, 107 were followed up 21 years later by clinical examination and by review of knee radiographs obtained with weight bearing. Seventy-nine of the 107 patients were men, and the mean age of the total study group at examination was 55 years (range 35-77). Sixty-eight sex- and age-matched individuals with healthy knees served as controls. RESULTS: Mild radiographic changes were found in 76 (71%) of the knees, while more advanced changes, comparable with a Kellgren-Lawrence grade of 2 or higher, were seen in 51 (48%). The corresponding prevalence values in the control group were 12 (18%) and 5 (7%), respectively. The relative risk for the presence of the more advanced radiographic changes representing definite radiographic tibiofemoral OA was 14.0 (95% confidence interval 3.5-121.2), using age- and sex-matched pairs for comparison. No correlation with sex, localization to compartment, type of meniscus tear, or work load was found. Knee symptoms were reported twice as often in the study group as in the controls. CONCLUSION: Surgical removal of a meniscus following knee injury represents a significant risk factor for radiographic tibiofemoral OA, with a relative risk of 14.0 after 21 years.