PURPOSE: the present study was conduced in order to analyse the molecular changes during the apoptotic cascade in knee articular cartilage of patients with OA. METHOD: articular cartilage specimens were assessed by histology (Haematoxylin and Eosin), histochemistry (Masson's Trichromic and Alcian Blue), immunohistochemistry through TRAIL, DR5 and Caspase-3, TUNEL and Hoechst staining in fresh isolated chondrocytes. RESULTS: histology results demonstrated the structural alterations in the articular knee cartilage with OA, and histochemistry results demonstrated the presence of matrix calcification and a proteoglycans reduction. Immunohistochemistry staining showed that structural alterations, matrix calcification and a proteoglycans reduction coincided with an increase in apoptotic cells when compared to normal cartilage; however, this cellular mechanism of death was demonstrated by TUNEL and Hoechst 33258 staining in fresh isolated chondrocytes. CONCLUSION: in this study, we demonstrated an apoptosis activation by the extrinsic pathway in OA cartilage. The apoptosis-positive cells might be due to a protection mechanism after sublethal injury, in particular, represented by an increased survival of chondrocytes that are able to participate in the repair process.