Neighborhood disadvantage, as indicated by low neighborhood socioeconomic status and poor social climate (e.g., low social cohesion), has been associated with a wide range of child and adolescent health and social problems. Evidence also indicates independent effects of neighborhood characteristics on drug use and sexual behavior. However, little research has examined the effect of neighborhood factors on the nexus between drug use and sexual behavior among adolescents. Informed by ecological theoretical frameworks, and using multivariate regression analyses, this cross-sectional study will examine the influence of neighborhood disadvantage (neighborhood poverty and low neighborhood social cohesion) on risky sexual behavior among a nationally representative sample of U.S. adolescents, including the potential mediating role of adolescent drug use. The study will also assess whether parental monitoring provides a protective effect against the influence of neighborhood disadvantage on adolescent drug use. Using data from the National Longitudinal Study of Adolescent Health (Add Health), the study will focus on two particularly risky sexual behaviors, exchanging sex for drugs or money and having multiple sexual partners. Previous research on exchanging sex for drugs or money and having multiple sexual partners has focused on examining individual-level characteristics and behaviors that predict these sexual behaviors. This study's conceptual framework is based on the premise that individuals' behaviors are influenced by their environment and that consideration of environmental context can improve understanding of associations between individual-level behaviors and health outcomes. Given the large and disproportionate burden of HIV/STIs among youth, understanding the individual and environmental factors that contribute to risky sexual behaviors in this population is critical. Examining neighborhood disadvantage will contribute to understanding the context that underlies adolescent drug use and risky sexual behavior and can inform more effective and comprehensive prevention strategies. This study will examine the influence of neighborhood disadvantage on risky sexual behavior among adolescents, including the potential mediating role of adolescent drug use. Understanding the environmental factors that contribute to adolescent drug use and risky sexual behaviors will inform more effective and comprehensive strategies to prevent these behaviors and their consequences, including HIV and other sexually transmitted infections. [unreadable] [unreadable] [unreadable]