Approximately 2 percent of parents reported high levels of problem drinking, and 1 percent reported problem drug use. If a broader definition of hazardous drinking was used, the proportion of teenagers exposed to parental drinking increased to just over 15 percent. When substance use was examined at a family level (taking account of alcohol and drug use among dependent children in addition to parents), the proportion of families experiencing some form of substance use was considerable. These findings have implications for both family and child care services, as well as for alcohol and drug treatment agencies. Agencies that serve children and families should be engaged in the identification of and intervention with parents who have alcohol or drug problems. Also, treatment agencies should address the parenting needs of their clients. Partnerships between treatment agencies and family support services would be beneficial in reducing parental substance use and its impact on dependent children. This study obtained data from the Belfast Youth Development Study (BYDS) and the BYDS Family Survey. Its objective is to examine the extent of problem alcohol and drug use within a community sample of parents and teenage children. The BYDS is an ongoing longitudinal study of adolescent alcohol and drug use in a single cohort of approximately 4,500 school children attending 43 postprimary schools in Northern Ireland. All interviews (i.e., parents and siblings) were conducted within the parents’ home. 1 figure, 6 tables, and 45 references