Osteoarthritis is one of the leading causes of disability in the elderly. The changes in the lubricating properties of synovial fluid lead to significant pain and loss of function. More than ten years have passed from the first studies. Up till now many authors have supported intra-articular hyaluronan (HA) therapy as not only a symptom-modifying therapy but also a treatment which may significantly decrease the rate of deterioration of joint structure. In this review we report data relative to knee and hip treatment. The ongoing studies continue to further our understanding of the fundamental mechanisms that likely underlie the therapeutic benefits of this treatment but, despite recent progress, many unresolved issues require further study. Large scale double blind controlled studies must be carried out to confirm these promising data and produce meaningful guidelines.