Background. Viscosupplementation is a relatively new method for the treatment of osteoarthritis (OA). The main goal of this project was to assess the safety and clinical utility of Hylan G-F20 (Synvisc(R)) in the treatment of pain associated with osteoarthritis of the knee. The type and frequency of additional therapies used during Synvisc(R) treatment were also assessed. It was a prospective project designed for monitoring Synvisc(R)-prescribing habits in usual medical care.<br /> Material and method. One hundred ninety knee joints in 187 patients were studied (OA symptoms were bilateral in 3 women). Synvisc(R) was indicated for the local treatment of pain in osteoarthritis of the knee. After the diagnosis, Synvisc(R) therapy was started at the recommended dose of 2 ml per intra-articular injection once <br /> a week (at 1-week intervals), three injections in total. The data collected, including medical history, physical examination, radiographic examination and treatment efficacy (overall assessment performed at each visit), were recorded on case report forms designed to facilitate statistical analysis. The physicians completed visual Analogue Scale (VAS) for overall assessment of OA pain at each visit. The clinical outcome was recorded after the end of therapy. The patient data were collected by physicians taking part in this project only.<br /> Results. In 156 cases (82.1%) either a substantial improvement or subsidence of symptoms was observed. In 34 cases (17.9%) the improvement was small or there was no change in the patient's condition. There were local adverse reactions in 2 patients (1.07%). There was no need to cease the treatment, to hospitalise a patient or to start any additional treatment. In 167 patients (89.3%) there was no need to start any non-pharmacological concomitant treatment.<br /> Conclusions. In summary, Synvisc(R) viscosupplementation should be rated among the safest and most effective methods for the treatment of OA, for it alleviates OA-related pain, thus reducing the need for NSAIDs and steroid injections. The use of Synvisc(R) in OA patients alleviates pain regardless of sex and age, the effect being the most pronounced in patients with low- and medium-grade radiographic changes.