The natural course after ACL injury is not well described in the literature. Every year about 7000 people, a majority aged 15-30 years old, injure their anterior cruciate ligament (ACL) in Sweden. About 3500 go through surgical treatment and rehabilitation. Despite the large amount of research on ACL-injuries, there are still many patients who have unsatisfactory outcomes regarding instability, decreased activity level, and quality of life, not being able to return to sport as well as an increased risk for osteoarthritis. The general aim of the study is to evaluate the natural course and recovery after ACL injury. Specific aims: