Tissue specimens from patients with Blounts disease were used to examine some biological and morphological aspects of the disease. In particular, we investigated the immunohistochemical characteristics of Blount patients cartilage as regards the extracellular matrix components. Some unexpected findings regarding the presence of bone sialoprotein, osteonectin, osteopontin, tenascin and fibronectin, in addition to the presence of various collagen types, led us to hypothesize an early ageing process in Blount patients cartilage with an abnormal tendency to mineralization. We made primary cultures of chondrocytes from patients to test if the reversion of mechanical in vivo conditions could normalize the cell proliferation and extracellular matrix deposition. Cell cultures failed to reverse the older phenotype that appears to be characteristic of Blount cell populations and confirmed their activity of synthesis of collagenic and non-collagenic proteins. In conclusion, some immunohistochemical and immunocytochemical aspects of Blount cartilage cells suggest an early tendency to mineralization of the extracellular matrix as compared with normal tissue.