Historical, geo-economic and behavioural perspectives are used in an exploratory analysis of China's migrant or 'floating' population as a factor in the spread of HIV on the mainland. Participants in the interview format survey (N = 506) included in-transit individuals in Beijing, and peddlers, restaurant workers, and employment seekers in Shanghai. When viewed in light of various social dynamics, the convenience survey data suggest that elements within this migrant population, as well as their rurally located partners and spouses, may be at increased risk of acquiring the virus. Given the sheer size and broad movement of this population, it is contended that it may well be a 'tipping point' factor in AIDS prevention and control in China.