Structural factors such as poor education, poverty, and gender and power inequalities are important determinants of young women's vulnerability to HIV infection. In The Lancet, Sarah Baird and colleagues report the results of a randomised controlled trial done with adolescent girls in rural Malawi, examining the effects of a cash transfer programme on risk of HIV infection. The investigators report that schoolgirls who received monthly cash payments of varying amounts were significantly less likely than girls who did not receive payments to be infected with HIV. Baird and colleagues' study provides a proof of concept that alteration of the structural environment with cash payments can affect HIV risk in young women.