Health registries and national health data bases can serve several purposes, including surveillance, evaluations of policy changes and “natural experiments” like pandemics and other outbreaks. Another useful approach is to combine analyses based on national databases with analyses from sub populations participating in cohort studies with questionnaire data and biological samples. Norway has the longest running birth registry in the world, and the possibility to link data from several national sources on an individual level. This allows for long term follow up of perinatal outcomes and birth characteristics, and the availability of IDs from parents enables use of family designs. Several examples will be presented.