Through the retrospective study of 1103 reconstructions of the anterior cruciate ligament (ACL) performed between 1984 and 1993, we try to outline the natural history of meniscal tears in acute lesions and in chronic insufficiency of the ACL. According to a more accurate evaluation of the clinical evolution, ACL-deficient knees can be classified into four different stages: acute, subacute, subchronic and properly chronic laxities. While acute injuries show a higher rate of lateral meniscus tears, chronic laxities are very frequently associated with severe medial meniscus lesions. Subacute and subchronic stages seem therefore to be the most favourable phases for ACL reconstruction, because of the lower percentage of severe associated meniscus tears and the minor risk of arthrofibrosis.