Although studies indicate school-based HIV/AIDS education programs effectively reduce risky behaviors, only 33 states and the District of Columbia in US mandate HIV/AIDS education. Ideally, school-based HIV/AIDS education should begin before puberty, or at the latest before first sexual intercourse. In 2011, 20% US states had fewer schools teaching HIV/AIDS prevention than during 2008; this is worrisome, especially for more vulnerable minorities. A nationally representative sample of 16 410 US high-school students participating in 2009 Youth Risk Behavior Survey was analyzed. Multiple regression models assessed the association between HIV/AIDS education and risky sexual behaviors, and academic grades. HIV/AIDS education was associated with delayed age at first sexual intercourse, reduced number of sex partners, reduced likelihood to have forced sexual intercourse and better academic grades, for sexually active male students, but not for female students. Both male and female students who had HIV/AIDS education were less likely to inject drugs, drink alcohol or use drugs before last sexual intercourse, and more likely to use condoms. Minority ethnic female students were more likely to have HIV testing. The positive effect of HIV/AIDS education and different gender and race/ethnicity effects support scaling up HIV/AIDS education and further research on the effectiveness of gender--race/ethnicity-specific HIV/AIDS curriculum.