The primary aim of the Prenatal Development Project (PDP) is to evaluate the developmental effects of prenatal exposure to steroid hormones and psychoactive drugs, particularly synthetic progestin, corticosteroids and barbiturates. Data collection has taken place at the Psykologisk Institut, now the Institute of Preventive Medicine, since 1981. The PDP database is unique for its breadth and depth as well as its combination of prospective longitudinal and cross-sectional perspectives. This article describes the database, including subject selection, perinatal information, the comprehensive contemporary evaluation and archival information from Danish registers. The unique matching procedures designed specifically for these projects and data analytic strategies are explained. The value of the PDP database is discussed both in relation to specific project aims (evaluating effects of prenatal drug exposure) and in relation to developmental and psychological research in general.