Migration is an important process of change for rural populations in developing countries. Migration is a primary cause of behaviour change -by their very act of migrating, migrants are different from those who do not migrate. The focus of the current study is male rural-urban migration in Tanzania and its interaction with sexual behaviour.The analysis presents results from a comparison with individual-level analyses of two populations, one (composed of recent rural-urban migrants) in an urban area and one in a rural area. Detailed migration histories (n=96 rural-urban migrants) and in-depth interviews (n=96 rural-urban migrants, n=51 rural residents) form the basis of the study. Three key research questions are addressed: How does the sexual behaviour of migrants differ from that of rural residents? How do HIV knowledge levels vary between rural-urban migrants and rural residents? What factors are associated with either intentions of behaviour change or reported behaviour? The results are counter-intuitive: rural-urban migrants -both married and unmarried -are not having sex in town. Despite limited understanding of the nature of HIV, the migrant population studied here regulates its behaviour in a way that reflects local understandings of the disease. This finding it important, not least because it challenges the view that HIV in sub-Saharan Africa is largely transmitted to rural areas by return migrants. Maasai rural-urban migrants in Tanzania -both married and unmarried -are not having sex in town. The policy and service provision implications of the results are explored.Abstract word count: 241