Abstract Objective: The purpose of this study was to assess the frequency of prenatal health-risk behaviors (substance use, sexual risk taking, and prenatal class attendance) among a nonrandom sample of first-time pregnant adolescents. Design: The design is descriptive. Sample: 145 ethnically diverse first-time pregnant adolescents aged 15–18 years. Measurement: Health behavior questions modified from the Center for Disease Control's Youth Risk Behavior Surveillance System. Results: The health-risk behavior most modified during pregnancy was alcohol use (64/145 drank but quit and 1/145 did not quit). Of the 52/145 who used street drugs, nine continued despite pregnancy. Of the 75/145 who smoked early in pregnancy, 39 continued. The majority did not use a condom at last sexual intercourse. Approximately half attended a prenatal class and half attended a teen parenting class. Conclusion: Health-risk behaviors captured by birth certificate data are thought to be underreported for all age groups, and the prevalence of health-risk behaviors in this sample of pregnant teens was often greater than the most recent national trend data available. The magnitude of the effects of health-risk behaviors on pregnancy outcomes necessitates improved data gathering to enhance planning and evaluation of research and interventions at community, system, and individual/family levels.