The prevalence of Rheumatoid Arthritis (RA) in Ireland has never been established. Studies from different countries show varying rates, being almost 100 per cent greater in the highlands of Scotland (10/1,000) than in rural Lesotho (6/1,000). A recent study also suggests a fall in the prevalence of RA among women in the London urban area. Given these variations the validity of extrapolating prevalence rates established for other countries to Ireland is questionable. This study aimed to establish a prevalence rate for RA in a defined Dublin population. A self-administered questionnaire was sent to 2,500 people chosen at random from the electoral register. The questionnaire was designed to select out both undiagnosed patients and those with definite arthritis. Respondents whose replies indicated an arthritic process, but in whom no diagnosis had been made, were asked to attend for further assessment and investigations as appropriate. Those who responded that they had been diagnosed with arthritis were asked for consent to inspect their hospital or general practitioner records. A diagnosis of RA was based on American Rheumatism Association (ARA) criteria. Valid responses were received from 1,227 people surveyed (response rate = 49 per cent). Six cases of RA were identified including 2 previously undiagnosed cases. A prevalence rate of 5/1,000 has been estimated based on these findings.