OBJECTIVE The pathologic matrix mineralization seen in calcium pyrophosphate dihydrate and basic calcium phosphate deposition diseases identifies a subset of osteoarthritis patients with an unusual joint distribution and rapid progression of disease. Several factors contribute to pathologic matrix mineralization, including changes in the extracellular matrix of articular cartilage. The factors contributing to extracellular matrix changes that promote crystal formation are important and not well understood. Better characterization of these factors will enhance the understanding of the pathogenesis of pathologic matrix mineralization and may identify potential targets for novel therapeutic interventions. RESULTS Histologic studies of cartilage from patients affected by calcium crystal arthritis show changes in the pericellular matrix of articular chondrocytes. The amounts and types of collagens, proteoglycans, and calcium-binding proteins are altered. The mechanisms by which these changes occur remain poorly understood. Recent work, however, has implicated alterations in the chondrocyte phenotype and post-translational matrix-modulating enzymes such as the transglutaminases. CONCLUSIONS Changes in extracellular matrix are associated with the pathologic matrix mineralization seen in calcium pyrophosphate dihydrate and basic calcium phosphate crystal deposition diseases. The literature on growth plate cartilage provides observations and mechanisms through which extracellular matrix contributes to normal matrix mineralization, and has served as a model on which to base studies in articular cartilage. More studies are warranted to enhance the understanding of how changes in extracellular matrix contribute to crystal deposition diseases.