Hyaluronic acid (Supartz®; molecular weight 620-1170 kDa) is a sterile, viscoelastic, non-pyogenic solution that is indicated as a medical device for the treatment of pain in patients with osteoarthritis of the knee who have failed to respond adequately to conservative nonpharmacological therapy and simple analgesics. Intra-articular injections of Supartz® were significantly more effective than control injections, according to an integrated longitudinal analysis of pooled data from five randomized, double-blind, vehicle-controlled, multicentre trials in patients with osteoarthritis of the knee. Supartz®, compared with the phosphate-buffered saline control, significantly reduced the total Lesquésne Index score in the post-injection period. Data from the individual trials demonstrated that the reduction in the total Lesquésne Index score was significantly greater than the control in two of the five studies. According to another efficacy endpoint (the mean reduction in the Western Ontario and McMaster Universities Osteoarthritis Index), which was assessed in only one of these trials, Supartz® was significantly more effective than the control in reducing the pain and stiffness subscale scores. Clinical scores of pain/inflammation and visual analogue scale (VAS) scores of pain during walking improved from baseline values for up to 6 months after treatment with Supartz® or a corticosteroid, with no significant between-group differences, in a small, randomized, open-label, multicentre trial in patients with osteoarthritis of the knee. Intra-articular injections of both Supartz® and Synvisc®, as well as a phosphate-buffered saline control, significantly reduced VAS scores of weight-bearing pain versus baseline after 26 weeks of therapy in a well designed trial; however, there were no significant differences between the three treatment groups. Neither hyaluronic acid formulation had a longer duration of clinical benefit than the saline control. Supartz® was well tolerated in patients with osteoarthritis of the knee. An integrated analysis of the five, well designed clinical trials demonstrated no significant difference between the Supartz® or control groups in the incidence of adverse events. The most common adverse events reported in Supartz® recipients were arthralgia, arthropathy/arthrosis/arthritis, back pain, nonspecific pain, injection-site reaction, headache and injection-site pain.