The electronic part of the nationwide Danish Psychiatric Central Register is now almost 25 years old. In this period it has proved its high value in administration, planning, treatment of patients, and not least in psychiatric research. Due to its national coverage, the register makes it easy to conduct epidemiological studies, such as analysis of trends, register linkage research, identification of representative cohorts for further analysis and follow-up studies of clinically identified cohorts. After many years of political turmoil, the register now seems to have assumed a more reasonable form, making allowance for both research interest and data protection. A proposed directive on the protection of medical data from the European Community may be a serious threat to the register and will probably eliminate all epidemiological and clinical research based on registers.