When a community-derived population of 840 rheumatoid arthritis patients was used to test the American Rheumatism Association's 11 diagnostic criteria for rheumatoid arthritis, these criteria divided patients into 3 reasonably distinct classifications (probable, definite, and classic). The severity of disease increased in direct proportion to the number of positive criteria. Three criteria involve invasive procedures that are rarely performed; they are unnecessary for effective use of the other 8 criteria. Although 256 possible combinations of these 8 criteria exist, the criteria function principally to classify patients into only 7 major clinical syndromes, each of which corresponds to a major clinical presentation. By identifying the logical interrelationships between criteria in this report, we have confirmed their applicability and provided insight into the manner by which criteria classify patients.