[Epidemiology of rheumatoid arthritis].

Although arthritis is a common disease in adults, only one in five new cases of arthritides is classifiable as rheumatoid arthritis (RA). The annual incidence of adult RA is about 0.05 per cent, and is ten times higher among women over fifty than among men under 50. The prevalence increases with age up to 70 years, after which it declines due to premature mortality. The high or low prevalences characteristic of certain populations may be explained by ethnic differences in genetic susceptibility.