In the digital neighborhood, Black and Hispanic youth communicate about many issues facing youth, 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 talk 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. The findings suggest participants who had previously had sex or who drank alcohol were more likely to post about sex or alcohol, respectively. Moreover, women posted more about sex generally and specifically about STIs, HIV, and pregnancy. Posts around sexual behavior often discussed trust in sexual partnerships and gendered views of sex. Posts linked alcohol and marijuana with stress relief and to cope with personal grief, community violence, and general distress. Understanding how youth think about sexual risk and substance use can inform the design of more effective prevention efforts.