The prevalence of arthritis is high, with osteoarthritis (OA) being one of the most frequent disorders in the population. In England and Wales, between 1.3 and 1.75 million people have OA and a further 0.25-0.5 million have rheumatoid arthritis (RA), while in France some 6 million new diagnoses of OA are made each year. In 1997, approximately 16% of the US population had some form of arthritis. This prevalence is expected to increase in the coming years, as arthritis more often affects the elderly, a proportion of the population that is increasing. The economic burden of such musculoskeletal diseases is also high, accounting for up to 1-2.5% of the gross national product of western nations. This burden comprises both the direct costs of medical interventions and indirect costs, such as premature mortality and chronic and short-term disability. The impact of arthritis on quality of life is of particular importance. Musculoskeletal disorders are associated with some of the poorest quality-of-life issues, particularly in terms of bodily pain (mean score from the MOS 36-item Short Form Health Survey of 52.1) and physical functioning (49.9), where quality of life is lower than that for gastrointestinal conditions (bodily pain 52.9, physical functioning 55.4), chronic respiratory diseases (72.7, 65.4) and cardiovascular conditions (64.7, 59.3).