The National Data Bank (NDB) for rheumatic diseases is a patient-based multi-disease, multi-purpose rheumatic disease registry that has been used primarily to study patients with RA, SLE, FM and OA. It enrols patients from the community, follows up with questionnaires and validates key patient data using medical records. Rheumatologist-written programs make NDB data immediately available to analysts. The NDB has been used to develop and validate diagnostic criteria, develop new questionnaires, describe illness and comorbid disease, assesses disease outcomes and the effect of therapeutic interventions, and measure costs and cost-effectiveness.