Data from a nationally representative household survey of South African youth aged 15-24 years found that sexually active men reporting anal intercourse were nearly twice as likely to be HIV infected as men reporting only vaginal sex (OR 1.7, 95% CI 1.0-3.0). The associated risk was more pronounced among men aged 15-19 years (OR 4.3, 95% CI 1.5-12.1). The association among women was not significant (OR 1.2, 95% CI 0.7-2.0).