Epidemiological research has good possibilities in Denmark due to the fact that all people have a personal PIN code and due to our many National health registers. In gynaecology the National Register of Patients, the Birth Registry, IVF-registry, Cancer Registry and latest the National Prescription Database offer unique possibilities of linking exposure data with many clinical outcomes. Danish epidemiology has contributed with morbidity analyses on children concieved by in vitro fertilisation, pharmacoepidemiological studies on short and long term effects of oral contraceptives and hormone therapy and, now, with routine assessment of clinical quality.