To date, Australia has only had an estimated 35,000 total HIV infections, which per capita is about four times less than the United States—and is a testament to the country’s early efforts to prevent spread in high-risk groups. But there’s one troubling exception to this success story: Prevalence of HIV continues to rise among men who have sex with men; it jumped 10% in 2012 and it has steadily increased since 1999. Given that roughly 70% of HIV-infected people in Australia receive treatment and that 90% of them have undetectable levels of virus in their blood, these increases in prevalence raise questions about treatment as prevention, which studies have shown can dramatically reduce the risk of transmission between heterosexuals. Does treatment have less of a preventive effect in men who are having sex with men? Is so, why?