A substantial body of recent research has focused on the prevalence of substance abuse among pregnant women, Its effects on maternal and infant health, ways to identify and effectively treat pregnant women, and the cost of care for pregnant women and their Infants. However, this research has been hampered by 8 lack of data, particularly at the state and local levels. The potential benefits of such research for improving treatment and other services to this high-risk group make it important to continue to develop accurate and timely data sources. This study builds on previous work that Inve!:tigated the quality of birth certificate and Medicaid data 8S well as previous efforts to merge these two data sources by augmenting the merged birth certificates and Medicaid data with data on a group of known substance abusers -those in substance abuse treatment. The purpose of merging these records is to Improve the identification of pregnant substance abusers and, more importantly, to provide an enriched data source of variables from all three sources. Using merged data from two example states, we show that linked birth certificates. Medicaid claims, and state substance abuse treatment files provide a useful source of information for studying the birth outcomes and costs for pregnant women In substance abuse treatment. However, certain groups, such 8S women who do not obtain any health care or substance abuse treatment, will be underrepresented in such a database. Consequently, efforts at more complete surveillance of pregnant substance abusers should be undertaken, perhaps through Increased efforts to improve reporting on the birth certificate, which is a universal document.