Biopsies of periarticular tissues from patients with episodes of chronic periarthritis were examinated by histological, ultrastructural and chemico-crystallographic methods. In all samples the mineralogical observations at the optical microscope, showed aggregates of microcrystalline incrustations, whose ultrastructural morphology has been characterized by SEM. The histological observations showed necrosis of collagen fibres and microcrystallization process in cavities and in metaplastic fibrocartilage. The HA deposits in the periarticular tissues, in the next stage of the process, are surrounded and demolished by macrophages and multinucleated giant cells. At the same time granulation tissue carries out the repair process, that begins with the formation of thin parallel collagen fibers interposed with many fibroblasts and numerous small vessels.