ARAMIS is a prototype of a national chronic-disease data-bank system consisting of parallel, longitudinal, clinical data sets from 17 diverse locations; the data describe the courses of thousands of patients with rheumatic disease followed over many years. Chronic-disease data-bank systems include the data themselves, protocols to ensure their quality, computer systems for their manipulation, statistical procedures for analysis and an appropriately skilled staff. Such a data resource facilitates analyzing long-term health outcomes and the factors associated with particular outcomes. Such systems are mandated by the overwhelming prevalence of chronic illness; the variability, complexity and uniqueness of a patient's course; the difficulties of traditional randomized approaches in these areas, and the time span required for studying these problems.