The Danish Psychiatric Central Register contains information dating from the 19th century; data were collected systematically from 1938. As of 1969 data on psychiatric admissions has been computerized and includes all admissions to psychiatric hospitals and psychiatric wards in general hospitals in Denmark, the Faroe Islands, and Greenland. Since January 1, 1995 information about all psychiatric outpatient contacts has been included. Among the advantages of the register are the close collaboration with the reporting hospitals and departments as well as its organization within the psychiatric epidemiological and social psychiatric research unit, Department of Psychiatric Demography. This has resulted in an intensive utilization of data from the register for research both in the department in other Danish and international research institutes the latter performed in collaboration with the department. Register research ranges from simple studies on prevalence to exploration of the longitudinal course in mental diseases, analyses of secular trends in different groups of disorders and recent linkage studies of risk factors for mental disorders. Recently, large data bases on the basis of data from The Psychiatric Central Register and from a number of other health related registers have been established. A linkage between The Psychiatric Central Register and various social registers is developing as is the development of quality assurance data bases.