This paper explores gender and mental health influences on alcohol, tobacco, and illicit drug use among late adolescent urban youths. Specifically, we examine whether rates of substance use differ by gender, whether mental health indices differ by gender and are predictive of substance use, and whether gender moderates the relationship between mental health and substance use. Data from our non-clinical sample of 400 youths were collected primarily online. Analysis of cross-sectional data revealed no differences in substance use by gender. Indices of mental health differed by gender, with girls reporting greater symptoms of depression and anxiety. Ratings of hostility were similar for boys and girls. Alcohol, tobacco, and drug use were associated with greater symptoms of depression, anxiety, and hostility; this relationship, however, was not moderated by gender. Study findings provide evidence that among late adolescent youths living in urban areas, poorer mental health status is associated with increased substance use. Evidence of a moderating effect of gender on the relationship between mental health and substance use was not significant.