This one-year study addresses a neglected topic in HIV research in Africa: the HIV prevention needs of female migrants. The study will address critical gaps in research on methods to obtain valid probability based samples of migrant women and to estimate HIV prevalence in this population at high HIV acquisition and transmission risks. It provides data needed to enhance the study "Identifying Opportunities for HIV Prevention Among Female Migrants in Western Kenya" (K01MH093205-02, Camlin), a qualitative study of factors that facilitate HIV risks among female migrants. This study will provide a platform upon which future interventions can be developed, by quantifying those risks, demonstrating feasibility of obtaining samples and estimating HIV prevalence in this under-researched and "hard-to-reach" population. It addresses these aims: 1) Pilot-test a method to collect a probability-based sample of highly mobile women, market traders, for an HIV prevalence, related risk behavior and demographic survey in Kisumu, Kenya; 2) Assess patterns of mobility and their associations with prevalent HIV infection in female market traders. The findings of this study will inform the development of an R34 proposal to support the design and evaluation of an HIV prevention intervention among female migrants. It will also will inform research on other populations of mobile women in Africa, whose mobility is often more complex and less well-measured than those of men. We will follow the sampling with an HIV prevalence, behavioral and demographic survey using voluntary counseling and testing, with referrals to HIV care and treatment. This study will therefore not only provide the first robust HIV prevalence estimates in a population at high HIV risk in western Kenya, where prevalence levels are among the highest seen globally; it will also provide testing and linkages to care for female migrants, for whom there are no existing targeted HIV initiatives in Kenya.