Gorbach PM, et al. - In a diverse cohort of young men who have sex with men (MSM), cannabis use, sexual behavior, and sexually transmitted infections (STIs) including human immunodeficiency virus (HIV) were assessed to establish the relationship between STIs and cannabis use. Every 6 months, the mSTUDY cohort conducted visits with 512 MSM between 2014 and 2017 in Los Angeles collecting demographics, sexual behaviors, and reports of frequency of substance use. MSM reporting only cannabis use had fewer STIs and lower risk sexual engagements than MSM reporting no drug or other drug use. Fewer MSM reporting only cannabis use had been incarcerated, had incarcerated partners, experienced interpersonal violence, and were HIV-positive when compared to those reporting no or other drug use.