Introduction: The Danish Twin Registry is a unique source for studies of genetic, familial and environmental factors on life events, health conditions and diseases.
Content: More than 85,000 twin pairs born 1870-2008 in Denmark.
Validity and coverage: Four main ascertainment methods have been employed. Completeness of ascertainment varies according to birth cohorts. For birth cohorts 1870-1930 both twins should survive to age 6 years. From 1931-1968 72% of all twin pairs has been ascertained, with complete ascertainment of all live born twins since 1968.
Conclusion: Because twins have been identified independent of traits and on a population basis, the Danish Twin Registry is well suited for studies to understand the influence of genetic and environmental factors for a wide variety of diseases and traits.