Degenerative changes of the knee joint are a well-known problem after ACL injury. In this study two groups of patients, one treated with ACL reconstruction (OP group) and one with conservative treatment (non OP group), were compared with reference to the development of arthritic signs after a mean follow-up of 77.9 (+/- 7.5). X-rays, taken at the time of the diagnosis of the ACL rupture and at follow up, were rated according to the classification described by Fairbank: 20% of the patients in the OP group and 50% in the non OP group showed no degenerative changes. The number of severe changes (grade III) was higher in the non OP group (18%) than in the OP group (4.5%). For patients in the non OP group a significant correlation was found between sports activity and the development of osteoarthritis. Meniscus pathology was seen to be a factor promoting the development of degenerative changes, but a significant correlation could not be found for either group.