The degree of cartilage changes by arthroscopic and radiologic examination was evaluated in a retrospective, cross-sectional study of 1012 patients with knee complaints at different times after knee injury. Patients were classified by age, sex, trauma date and type of injury. The condition of the cartilage was graded on a 1-10 scale based on findings at arthroscopy and on weight-bearing radiographs. Patients with injury to the anterior cruciate ligament (isolated or combined with injury to meniscus or collateral ligaments) showed the first radiologic signs (joint space narrowing) of osteoarthritis (OA) at an average age of about 40 years, while patients with isolated meniscus injury had the same stage of disease at an average age of about 50 years. Both study groups displayed the first radiologic signs of OA on average about 10 years after the injury and showed increasingly serious arthroscopic and radiologic signs of joint damage with increased time between injury and examination. For patients who sustained an isolated meniscus injury between the ages of 17 and 30, the average time until development of radiologic signs of OA was about 15 years, while for those who had the same injury over the age of 30, the corresponding time interval was only about 5 years. We conclude from this that knee OA becomes increasingly severe with increased time between joint injury and examination. OA changes appear sooner in older patients with knee injury than in the young.