Introduction: An anterior cruciate ligament (ACL) rupture is a common injury of the knee. An ACL rupture may be caused by sports with pivoting movements. Common symptoms after an ACL rupture are pain and instability. In case of instability and the patient’s desire to return to the same sport level an ACL reconstruction can be performed. From literature it is known that an ACL reconstruction may influence the development of arthritis. However, it is still unclear whether there is a relation between the timing of the ACL reconstruction and the development of arthritis in the long term. Objective: Primary objective is to investigate if there is a relation between the timing of ACL reconstruction and the degree of arthritis after a long time. Secondary goal is to determine the intra- and inter-rater reliability of the osteoarthritis classification (Kellgren and Lawrence). Other secondary objectives are to determine the long-term results of physical function and sport activity level after ACL reconstruction. Methods: This is a retrospective study with two cohorts. Cohort one had underwent ACL reconstruction within one year after the trauma (N = 42) and the second cohort had it done between five and ten years after the trauma (N = 37). All patients were recalled for a new x-ray of the knee joint and for an appointment at the orthopedic outpatient clinic, where a physical examination took place. The degree of arthritis is determined by means of the Kellgren and Lawrence classification. Three observers judged twice the X-rays made at the time of ACL reconstruction and the X-rays made at follow-up, double blinded. During the clinical appointment, a number of questionnaires were filled in: the KOOS and the IKDC to determine the physical functioning, and CKRS and the Tegner to determine the sport activity level. Results: The intra-and inter-rater reliability for assessing the radiographs is considered to be good. Analyses of the X-rays show no significant difference in the degree of arthritis between the two cohorts after a mean follow-up of 10 years. However, cohort 1 had significantly less arthritis compared to cohort 2 at the time of the ACL reconstruction. Physical functioning was not significantly different between the two cohorts after a follow-up of 10 years after ACL reconstruction. The sports activity levels both within and between the two cohorts decreased significantly after a follow-up of 10 years. Conclusion: The degree of arthritis between the two cohorts was not significantly different, suggesting that the timing of the ACL reconstruction does not influence the degree of arthritis. However, the degree of arthritis was lower for cohort 1 at the time of ACL reconstruction. That might be an indication that the time interval between the trauma and ACL reconstruction might influence the initial degree of arthritis. However, the degeneration process has not been slowed down after the reconstruction, since there is no difference in the degree of arthritis on the long term.