There is a widespread assumption in Northern Karnataka, India that HIV transmission is due to the large volume of male seasonal labour out-migration. In order to examine this issue, an ethnographic study was conducted in one of the Northern Karnataka districts using a combination of quantitative and qualitative methods. Findings indicate that migration does not seem to be a key factor affecting sexual behaviour among married men. Nearly 35% of married migrant men reported being involved in extramarital sex and 40% of unmarried migrant men were involved in premarital sex. While earlier in the epidemic there was a strong correlation between HIV infection and migration, more recently the correlation seems to be getting weaker. More innovative HIV prevention programmes which take into account the social and cultural characteristics of this region are urgently needed to curtail the rapid development of the epidemic.