Printed in Great Britain A Cross-National Epidemiological Resource: The Swedish and Finnish Cohort Studies of Like-Sexed Twins

Two large-scale studies of adult like-sexed twin pairs are ongoing in Sweden and Finland. Both studies comprise an unselected series that has been studied in a comparable fashion. Zygosity determination and health questionnaire data-gathering were carried out in 1973 for the Swedish study and in 1975 for the Finnish study for the comparable age groups. Data on hospital usage, cancer incidence and mortality are collected by record-linkage from the respective national registries. Cross-national twin studies can permit testing of hypotheses of the relation-ships between genetic and cultural factors and major chronic diseases and their risk factors. In studying the role of different factors in the aetiology of a disease, relationships are strengthened if they are found to exist in different populations. International comparisons of aetiological studies of chronic diseases illustrate the usefulness of this approach in epidemio-logical research.1'2 This paper will describe the structure of two nation-wide twin cohorts covering adult like-sexed twins, the Swedish and the Finnish Twin Cohort Studies, an