Objective - Epidemiology is in focus of attention these years. Psychiatry pioneered the development of epidemiological methods and their application in research and planning. Psychiatric epidemiology has been preoccupied with the secondary health service, i.e. the hospital-based service. The aim of the present paper is to discuss which monitoring systems and which types of data will be needed in the future. Method - The discussion is based on experience and results from existing psychiatric registers, mainly the Danish Psychiatric Case Register at the Department of Psychiatric Demography in Aarhus. Results - Some countries have developed monitoring systems to routinely record data on activities in the hospital sector, which is highly beneficial to quality assurance, research, and planning. However, after the introduction of decentralized psychiatry it is necessary to acknowledge the urgent need to move the focus for the employment of epidemiology to benefit also the activities in community psychiatry and in the primary mental health care sector. Though it involves great difficulties, monitoring systems to collect valid and reliable information from these systems of care must be developed. It is also necessary to develop epidemiological methods to be employed in research and quality assurance within this field. Such research methods should be used, not only in the exploration of the aetiology, course and clinical outcome of psychiatric disorders, but also when observing, for example, the social functioning and disability of psychiatric patients, the need for care, the meeting of needs, the health economy and patient flow between the different levels of the system of treatment. This results in large demands on data security, legislation and ethics for the collection and employment of data in the epidemio-logical models. Conclusion - It is recommended to give priority to extended utilization of existing register data; establishment of secondary mental health care registers in countries without such facilities; establishment of primary mental health care registers; establishment of disability monitoring systems; establishment of systems to monitor patients' resources; extended collaboration in this work between psychiatric epidemiologists, administrators, economists, and technicians.