This study uses data from the 2004-05 Tanzanian Demographic and Health Survey to examine whether men’s traditional gender role attitudes contribute to their sexual risk behaviours for HIV. Logistic regression with random effects were used to analyze effects on risk behaviours at last sex (partners being drunk and condom use) with the three most recent sexual relationships. Men’s traditional gender attitudes increased risky sexual behaviours (e.g., not using a condom) even when they had accurate knowledge regarding HIV risks. The impact of men’s gender attitudes and HIV knowledge on risky sexual behaviours did not vary by relationship type. Unexpectedly, condom use was more likely when either partner was drunk compared to neither being drunk, though the protective impact of HIV knowledge remained. Overall, these findings suggest that traditional gender attitudes present barriers to preventing HIV/AIDS that even increased knowledge about HIV risks may not overcome.