Sierra Leone suffered from 11 years of civil war (1991-2002) resulting in tens of thousands of deaths and mutilations and massive population displacement. In 2001, ARC International, Sierra Leone, conducted a baseline survey of 244 female youth and 293 male youth on knowledge, attitudes, and behaviours around HIV/AIDS and STIs in Port Loko. In 2003, following 2 years of HIV prevention activities, a comparable post-intervention survey of 250 female and 299 male youth was performed. Comparison of baseline and post-intervention results showed that HIV/AIDS knowledge increased dramatically among both groups, with those able to name three effective means of avoiding AIDS increasing from 4% to 36% among female youth, and 4% to 45% among male youth. Reported condom use at last sex increased among female youth from 16% to 46% and among male youth from 16% to 37%. These results demonstrate that, despite the challenges inherent in a post-conflict country, good quality AIDS prevention programmes can be successful.