Despite concern over the co-occurrence of substance use and unplanned pregnancy among adolescents, little information is available about drug use before and during pregnancy in adolescence. The present study examined substance use among a sample of premaritally pregnant adolescents (n=241) who were interviewed as part of an ongoing longitudinal study of patterns of drug use among pregnant and parenting school-aged adolescents. Urine samples were obtained from a randomly selected 50% subsample and laboratory analyzed to verify self-reported substance use (2.5% had discrepant data). Respondents were on average 16 years old; 51% were white and 32% were African American. Findings indicated that, although the majority of respondents had a history of substance use, substance use declined substantially during pregnancy. Multiple regression analysis indicated that boyfriend's substance use and best friend's substance use during the previous month, the respondent's perceived harm of substance use during pregnancy, and being a school dropout were related to the respondent's substance use during the previous month, while pregnant. The findings have implications for substance use prevention and intervention programs for pregnant and parenting adolescents. (Author)