Purpose:Among a sample of adolescent girls, we assessed: 1) prevalence of sexual harassment by type, place of occurrence, and perpetrators; 2) association with substance use and poor mental health outcomes; and 3) the proportion of girls experiencing sexual harassment in more than one place and relation to study outcomes. Methods:We collected survey data from 159 sexually active girls (aged 15-19 years) recruited from an urban health clinic in Southern California. We used multivariable regression models to assess associations between sexual harassment in the past 6 months and the following outcomes: 1) substance use in past 30 days (alcohol use, binge drinking, and marijuana use, respectively); 2) other drug use ever; and 3) feelings of depression and anxiety, respectively, in past 30 days. Results:Almost two-thirds of girls (65.4%) reported experiencing sexual harassment in the past 6 months. Among those reporting recent harassment (n = 104), the abuse most frequently occurred in public spaces (on public transport [50.5%], at school [42.7%], and in their neighborhoods [39.8%]) and most often in the form of sexual comments, jokes, or gestures (57.2%), although 12.6% were "touched, grabbed, or pinched in a sexual way." The vast majority (82.7%) did not know the perpetrators (82.7%). Experiences of sexual harassment in the past 6 months were significantly associated with alcohol use (odds ratio [OR], 4.5; 95% confidence interval [CI], 2.0-10.2), binge drinking (OR, 4.2; 95% CI, 1.8-9.8), and marijuana use (OR, 2.6; 95% CI, 1.2-5.7) in the past 30 days; other drug use ever (OR, 5.4; 95% CI, 1.8-16.4); and feelings of depression (OR: 2.7; 95%CI: 1.3-5.5) and anxiety (OR: 2.6; 95%CI: 1.2-5.5) in the past 30 days. Just over half (55.3%) reported sexual harassment in more than one place, which was also associated with poor substance use and mental health outcomes. Conclusions:Findings suggest that sexual harassment experiences are pervasive, occur in girls' immediate and everyday environments, and are associated with girls' substance use and adverse mental health outcomes.