Background and purpose - Until now, there have been no studies beyond 30 years after anterior cruciate ligament (ACL) reconstruction. We report knee function a mean 31 years after ACL reconstruction.Patients and methods - This cohort comprised a case series of 60 patients with a mean follow-up of 31 years (28-33) after ACL reconstruction. Patients were evaluated with the International Knee Documentation Committee (IKDC) objective assessment, Knee injury Osteoarthritis Outcome Score (KOOS), Tegner Activity Scale, radiography, and MRI.Results - 30 patients showed an intact ACL graft and 30 a ruptured or missing ACL graft. 40 patients had osteoarthritis in the tibiofemoral compartment and 24 patients in the patellofemoral compartment. Patients with intact ACL grafts scored higher than those with ruptured or missing ACL grafts when it comes to KOOS Sport/Rec. The Hodges Lehmann estimated median difference between groups was 15 (95% CI 0-35). The KOOS scores were lower in the group with ruptured or missing ACL grafts when compared with a healthy-knee reference group of males in terms of Pain, mean difference -8 (CI -15 to -1), Symptoms, mean difference -18 (CI -27 to -9), and Sport/Rec, mean difference -21 (CI -34 to -8). In the group with intact ACL grafts, the KOOS score was lower than a healthy-knee reference group of males in terms of Symptoms, mean difference -12 (CI -21 to -3). Scores for all subgroups of KOOS were higher in patients without osteoarthritis. The IKDC overall clinical assessment outcome was worse in patients with a ruptured or missing ACL graft. The Hodges Lehmann estimated median difference between groups was 1 (CI 0-1).Interpretation - Patients with an intact ACL graft reported higher sports activity and recreation, as measured with KOOS, than patients with a ruptured or missing ACL graft. Patients with severe osteoarthritis reported lower sports activity and recreation, as measured with KOOS.