Nordic registers offer internationally unique possibilities for psychiatric research. We aim here to describe Nordic health and social registers and to review selectively certain psychiatric epidemiological studies that have utilised these registers. Investigations into admission rates have also been carried out using nationwide hospital registers, and incidence and prevalence rates have often been elucidated by means of register data in combination with interviews and case notes. Registers from early life, such as birth and school registers, have been used as a source for exposure variables, employing various outcomes based on register or interview information. The registers have enabled hypotheses to be tested which otherwise would have been difficult to study reliably, for example due to rare events or disorders, or because of the need to study lifespan developments. The combining of various registers within and between countries can be expected to provide further possibilities to study novel topics in the future.