Based on compulsory notification and operative since 1967 the Medical Birth Registry of Norway comprises all births in the country after 16 weeks gestation. The notification form is filled in by the midwife and the doctor and contains civil data on mother, father and the newborn as well as medical data on mother's health before and during the pregnancy, on the birth, including complications, and on the newborn, including birth defects and other congenital conditions. All diagnoses recorded before discharge from the hospital are included. From 1998, diagnoses recorded after transfer to a paediatric department and throughout the first year of life are notified as well. The registry data are used for epidemiological surveillance of birth defects and other perinatal health problems, for evaluation of health services and as a basis for perinatal epidemiological research; follow-up studies based on internal and external record linkage are essential.