This paper presents findings from qualitative research carried out by the CARAM Southeast Asia Research Network in the period 1997-1999. In several countries in Asia, interviews and focus group discussions were held with migrant workers about their working conditions, access to health care, and factors affecting vulnerability to HIV/AIDS. Factors that have an impact on migrants' sexual behaviour include the country of destination and the availability of a commercial sex sector. Cultural differences with respect to sexual behaviour are also important. As social control in migrant communities is often limited, sexual relationships that are prohibited at home are often possible abroad. Besides continuing to belong to their home communities, migrants gradually adapt to their new communities abroad. In so doing, they adopt a so-called 'migrant identity' which can lead to a denial of certain (sexual) behaviours. This can make them difficult to reach by means of conventional HIV/AIDS prevention approaches.