We describe the aims and uses of a large rheumatological database, the national database of the German Collaborative Arthritis Centres. The database is a continuing registry of all patients with inflammatory rheumatic diseases seen at one of the member sites of the German Collaborative Arthritis Centres. The patients are recorded once a year with a clinical datasheet and a patient questionnaire. The database has been used for identification of deficits and trends in health care, description of current treatment practices, practice variations and individual burden of diseases, as well as for quality assessment. Large differences in disease modifying antirheumatic drug treatment between rheumatologists and nonspecialists as well as deficits in nonmedicinal therapies were identified. Considerable practice variation in German rheumatology with respect to drug and nondrug therapies was identified. The burden of disease (pain, disability, early retirement) was high in various patient subgroups. The database is useful for various aspects of health services research. It has, however, the important limitation that no specific followup procedure is applied. Therefore, longitudinal data exist only for patients in continuing rheumatological care.