The nationwide Swedish Medical Birth Register (MBR) includes more than 98% of all births in Sweden since 1973. The MBR is updated annually, and is based on information from antenatal, obstetric, and neonatal records. Maternal information includes self-reported medical history, socio-demographic factors, smoking and snuff use, medication use, height and measured weight. Birth and neonatal/postpartal data include birth date, mode of delivery, singleton or multiple birth, gestational age, stillbirth, birth weight, birth length, head circumference, infant sex, Apgar scores, and maternal and infant diagnoses/procedures. The overall quality of the MBR is very high, partly due to the semi-automated data extraction from the standardized regional electronic health records. The MBR can be linked to other health registers through the unique personal identity numbers of mothers and live-born offspring. More than 1000 scientific publications have used MBR as a data source.