Clients of female sex workers (FSWs) serve as "bridging population" transmitting HIV from high risk groups to general population.This study aims to estimate the prevalence of having sex with FSWs among males aged 15-49 and to describe some HIV related behaviors among those male. The sample size included 1804 men in three cities, Hanoi, Da Nang and Can Tho in 2010. Of this sample, 6.9 percent of the sexually active men admitted that they have ever had sexual relation with FSW. This prevalence is highest in Hanoi and lowest in Da Nang. The prevalence of having sex with FSWs is higher among male in urban, male with higher education and better socio-economic status. High risk behaviors among males are alarming, only 51.5 percent used condom in the most recent sexual encounter with FSWs and 42.4 percent clients have multiple partners during the last 12 months. Program implementers as well as policy makers in the area of HIV prevention should pay more attention to the condom efficacy, condom use and related stigmatized issues.