The association of migration with AIDS in sub-Saharan Africa is well documented, yet the social and behavioral mechanisms underlying this relationship remain poorly understood. Using data from the 1993 Kenya Demographic and Health Survey, this article examines whether migrants are more likely than nonmigrants to have multiple recent sexual partners and not use condoms with those partners. Results indicate that migration is a critical factor in high-risk sexual behavior and that its importance varies by gender and by the direction of movement. Independent of marital and cohabitation status, social milieu, awareness of AIDS, and other crucial influences on sexual behavior, male migrants between urban areas and female migrants within rural areas are much more likely than nonmigrant counterparts to engage in sexual practices conducive to HIV infection. In rural areas, migrants from urban places are more likely than nonmigrants to practice high-risk sex. Given the predominance of men in urban migration and the large volume of circulatory movement between urban and rural areas, these results have serious implications for HIV transmission throughout Kenya.