Sexual and racial minority adolescents and young adults account for the most substantial number of new HIV infections in the United States. Numerous publicly available websites and YouTube videos contain HIV/STI prevention information that is culturally tailored to racial and ethnic minorities, and gay and bisexual youth. However, the effect of this easily accessible Internet content on adolescent and young adult HIV/STI related knowledge, attitudes and behaviors is unknown. We assembled a HIV/STI Internet intervention from publicly available online sources, including YouTube and privately and publicly hosted websites. We tested the preliminary efficacy of this internet intervention by means of a randomized controlled pilot study with 60 diverse adolescents and young adults recruited in Providence, RI (mean age 18.6 years, 62% male, 52% Black/African American, 36% Hispanic, 47% non-heterosexual). Youth who received links to publicly accessible online prevention content by email had a significant improvement in HIV self-efficacy (p < .05) and a significant reduction in unprotected vaginal or anal sex (12.5 vs. 47.6%, AOR = 7.77, p < .05), as compared to a control group who did not receive the internet content by email. If these preliminary findings can be confirmed by future research, free online content could be inexpensively distributed to at risk youth in underserved communities and could hold promise as an inexpensive method of HIV/STI prevention.