The Norfolk Arthritis Register (NOAR).

The Norfolk Arthritis Register (NOAR) has been recruiting and following patients with early inflammatory polyarthritis (IP) since 1989. Approximately three-quarters of the patients followed satisfy classification criteria for rheumatoid arthritis (RA) by 5 years from symptom onset. This paper summarises the publications which have been based on the NOAR cohort with respect to the incidence and prevalence of IP and RA, genetic and environmental risk factors for the development of IP, outcome following the development of IP and predictors of outcome. It also discusses methodological issues in examining the treatment effect in observational cohorts and the costs to the healthcare system of patients with early IP.