Clinical assessment of established rheumatoid arthritis (RA) can have several purposes. It can be used to evaluate prognosis, disease course or interventions at both the individual and the group level (i.e. in a clinical trial), over the short or long term. The instruments used for the different purposes are not always the same. For example, information on prognosis is very useful when assessing the risk:benefit ratio of early aggressive pharmacotherapy; however, established prognostic factors are currently of limited use in individual patients with established RA. As, at the individual patient level, disease activity, disability and joint damage have variable courses, the course of the disease should be evaluated regularly both with process (i.e. erythrocyte sedimentation rate, joint counts) and with outcome (i.e. radiological progression, sum of past process) measures. For the evaluation of interventions, 'core sets' of valid measures to assess disease activity, outcome and specific criteria for improvement are used; these can, to some extent, be useful in clinical practice.