In the digital neighborhood, Black and Hispanic youth communicate about issues they face, including sex and substance use. This population of young people is also disproportionately burdened by negative consequences associated with sex and substance use behaviors even when their behavior is less risky. Given the increased likelihood of negative outcomes, we investigated how young people communicate about these behaviors in their digital social networks. This mixed methods study integrates a behavioral survey with a machine learning supported, qualitative content analysis of one year of Facebook and Twitter posts from 50 Black and Hispanic youth, with feedback from a youth advisory board. Participants who had previously had sex or drank alcohol were more likely to post about sex or alcohol, respectively. Moreover, compared to male youth , female youth posted significantly more about sex in general and about STIs, HIV, and pregnancy . Posts about sexual behavior often discussed trust in sexual partners and gendered views of sex. Posts linked alcohol and marijuana with stress relief and coping with grief, community violence, and distress. Understanding how youth think and communicate about sexual risk and substance use can inform the design of effective prevention efforts.