THE DANISH TWIN REGISTER

Background: Population based twin registers represent a valuable tool for genetic epidemiological research, since twin studies aim at separa ting the effect of genes and environment for complex traits. The Danis h Twin Register's history, size, ascertainment and completeness of dat a, as well as data accessibility and availability are described. Resul ts: The Danish Twin Register comprises 14,051 twin pairs born 1870-193 0, representing all twins surviving to age six years, and 20,888 twin pairs born 1953-1982, representing 75% of those born 1953-1967 and 95% of those born 1968-1982. The birth cohorts 1931-1952 og 1983-1993 are being ascertained at the moment. The register is available for resear ch given certain conditions are fulfilled. Conclusion: This register w ill in a few years be the most comprehensive twin register in the worl d. It is a very valuable Danish research resource.