In a pioneering study undertaken in Pakistan, urban men's sexual behaviors, perceptions and knowledge regarding sexually transmitted infections including HIV/AIDS were determined by employing both qualitative and quantitative research methods. Focus group discussions were carried out initially and followed by a structured cross sectional survey that interviewed 2400 men in six cities. While most men (90%) had heard of the term HIV/AIDS however nearly a quarter of the respondents had misconceptions regarding its mode of transmission. HIV/AIDS was generally perceived as a disease acquired by indulging in "immoral" activities. Knowledge regarding other sexually transmitted infections was negligible. The results from this study point to the need for developing awareness campaigns in Pakistan that mitigate stigma and reduce vulnerability. (Contains 4 tables and 1 figure.)