The Avon Longitudinal Study of Parents and Children (ALSPAC, and also known as the 'Children of the 90s' study), which is based at the University of Bristol, is an ongoing longitudinal study of a population of children born to mothers resident in one geographic area in England. The overall objectives of the study are to understand the ways in which the physical and social environments interact over time with genetic inheritance to affect health, behaviour and development in infancy, childhood and then into adulthood. Information has been collected at regular and frequent intervals from pregnancy and throughout childhood concerning the child's physical environments, parental characteristics (including economic and educational indicators), social circumstances, and family relationships. ALSPAC recruited more than 14,000 pregnant women with estimated dates of delivery between April 1991 and December 1992, who were living in the Avon Health Authority area, to take part in the study. These women, the children arising from the index pregnancy and the women's partners have been followed up since then and detailed data collected throughout childhood.The datasets held at the UKDA are sampler datasets, and have been compiled using various questionnaire and assessment data from the ALSPAC study. Further information may be found in the documentation, and for the wider study, on the ALSPAC web site.