The 2004 outbreak of influenza A H5N1 and the WHO's recommendation for national pandemic plans has led the Thai Ministry of Public Health to develop an influenza vaccination programme for high-risk adults. To date there is no available information to guide this intervention, and how to maximize the uptake of the vaccine by the Thai population. To address this knowledge gap, this study explored factors influencing urban-dwelling Thai adults' decisions whether or not to have the vaccine. It explored their beliefs about influenza and influenza vaccination, and other influences on their decisions.