This retrospective study aimed to provide data on the prevalence, epidemiology and etiology of the knee articular cartilage lesions and describe and estimate, on the ground of a large database, the number of patients who might benefit from cartilage repair surgery. The analysis of 25,124 knee arthroscopies performed from 1989 to 2004 was conducted. Information concerning cartilage lesion, associated articular lesions and performed procedure were collected. Cartilage lesions were classified in accordance with the Outerbridge classification. Chondral lesions were found in 60% of the patients. Documented cartilage lesions were classified as localized focal osteochondral or chondral lesion in 67%, osteoarthritis in 29%, osteochondritis dissecans in 2% and other types in 1%. Non-isolated cartilage lesions accounted for 70% and isolated lesions accounted for 30%. The patellar articular surface (36%) and the medial femoral condyle (34%) were the most frequent localization of the cartilage lesions. Grade II according to Outerbridge classification was the most frequent grade of the cartilage lesion (42%). The most common associated articular lesions were the medial meniscus tear (37%) and the injury of the anterior crucial ligament (36%). Articular cartilage lesions are a common pathology of the knee joint. The potential candidates for cartilage repair surgery, patients with one to three localized grade III and IV cartilage lesions, under the age of 40 were found in 7% and under the age of 50 years in 9% of all analysed patients. However, because these patients are a heterogeneous group and the natural history of cartilage lesions remains so far unknown, also the total number of patients in our study, who might benefit from cartilage repair, remains unknown precisely.