Despite concern over the co-occurrence of substance use, unplanned pregnancy and other problem behaviors in adolescence, little information is available on substance use before, during, and after adolescent pregnancy. The authors report data from the first 100 Ss enrolled in an ongoing longitudinal study on drug use before and during pregnancy in adolescence. Unmarried pregnant adolescents, ages 17 and under, were recruited for the study from urban alternative school programs and community social and health service agencies. Findings indicate that although lifetime prevalence of drug use was relatively high and pregnant respondents appear embedded in drug prevalent environments, substance use declined voluntarily and substantially during pregnancy. Prepregnancy drug use predicted substance use during pregnancy, but neither best friends' nor boyfriends' use of alcohol or marijuana predicted subjects' use of these substances during pregnancy after taking prepregnancy use into account.