ACL-reconstruction aims to restore joint stability and prevent osteoarthritis; however, malfunction and osteoarthritis are often the sequelae. Our study asks whether ACL-reconstruction or conservative treatment lead to better long-term results. In this retrospective cohort study, 136 patients with isolated ACL-rupture who had been treated by bone-ligament-bone transplant or conservatively were identified. Twenty-seven of these were excluded because of a revision operation in the 11.1 years follow-up period, leaving 109 patients (60 reconstructions and 49 conservatively treated) for evaluation based on clinical, radiological and internationally accepted knee-scores (Tegner, IKDC, Kellgren and Lawrence). An individual cohort study is classified as EBM level 2b according to the Oxford Centre of EBM. We observed significantly better knee-stability (P = 0.008) but more osteoarthritis (Grade II or higher) after ACL-reconstruction (42% vs. 25%). Physical activity levels were similar in both groups during the follow-up period (P = 0.16). Eleven years after ACL-rupture the physical activity levels are similar for both groups. After ACL-reconstruction, stability is higher as is osteoarthritis, whereby the result is not necessarily perceived as better subjectively. Specifically, this retrospective study yielded a 24% incidence of oseoarthrits 11 years after conservative management of ACL-rupture in patients not needing secondary surgery. The risk of secondary meniscal tears is reduced after ACL reconstruction, which reduces the negative effects of OA after surgery. The ultimate objective would be to achieve a good subjective outcome by conservative treatment followed by a rehabilitation program designed to keep secondary meniscus tears at a low level.