Studies on the spread of AIDS were quick to point to geographical mobility as one of the factors perpetuating thespread of HIV (Hunt, 1989; Anarfi, 1993; Kane et al., 1993; Pison et al., 1993). In Sub-Saharan Africa, where HIV ismainly transmitted by sexual intercourse, it is generally postulated that migrants tend to adopt high-risk sexual behaviourat their place of destination, thereby exposing both the contact population and themselves to infection. It is also believedthat migrants continue with such behaviour on their return, aided by the force of attraction they exert on women of theircommunity, thanks to their income which is higher than that of non migrants (Anarfi, 1993; Chirwa, 1997). Migrantspose an additional threat to their communities of origin because of the risk of infecting their spouses, thereby spreadingthe disease within their extended families in situations where levirate and sororate are practiced1. One of the modelsmentioned in the literature explains the greater propensity of migrants to adopt high-risk sexual behaviour through theirlow perception of the risks and consequences inherent in their behaviour. This low perception, it would appear, resultsfrom pre-migration factors which make them more daring (age, sex, marital status, education, etc.), factors resultingfrom migration (separation from spouse or regular partner) and, finally, from the contact with a new environmentconsidered stressful and more sexually permissive (Brockerhoff and Biddlecom, 1998). This paper seeks to test thismodel using the case of migrants from the River Senegal Valley, one of the high-mobility regions of the country and oneof the hardest-hit by the epidemic. In this regard, we will be looking at migration trends inside Senegal during the 1985– 2000 period, that is, since the first cases of HIV/AIDS were reported in the country2. The paper rounds off byexamining the implications of the findings for research and prevention strategies.