Exposure during fetal life may have long-lasting health consequences for the child. Cohorts with biological material are necessary to investigate the possible biological mechanisms behind this potential early programming of disease. The Aarhus Birth Cohort Biobank was established in 2008 as an amendment to an ongoing research database, the Aarhus Birth Cohort. It aims to provide the opportunity to investigate the role of genetic factors, environmental exposures and lifestyles in pregnancy on the risk of disease in the offspring. All pregnant women who plan to give birth at Aarhus University Hospital, Skejby, and the fathers-to-be are invited to participate in the Aarhus Birth Cohort Biobank. Blood samples (mother 54 ml, father 4 ml) are drawn at the time of the routine ultrasound scanning in gestational week 12. At the same time, the women fill out a detailed questionnaire on medical and lifestyle factors. Immediately after birth, blood (10 ml) from the umbilical cord and umbilical cord tissue are sampled. Samples from the mothers are separated into plasma, buffy coat, erythrocyte suspension and serum before freezing at -80°C. Samples of whole blood are also stored, from both the mother and the father. Plasma, buffy coat, erythrocyte suspension and tissue from the umbilical cord are stored at -80°C. All researchers can apply for access to the database. For more details, see www.ab-biobank.dk or email@example.com.