Although the dire life circumstances of labor migrants working in Russia are well-known, their HIV risk vulnerability and prevention needs are understudied. Low socioeconomic status, lack of access to services, separation from family, and limited risk awareness all contribute to migrants' HIV vulnerability. Male labor migrants in St. Petersburg (n = 499) were administered assessments of their sexual behavior practices, substance use, and psychosocial characteristics related to risk and well-being. Thirty percent of migrants reported multiple female partners in the past 3 months. Condom use was low, ranging from 35% with permanent to 52% with casual partners. Central Asian migrants had very low AIDS knowledge, low levels of substance use, moderate sexual risk, high depression, and poor social supports. Eastern European migrants had higher AIDS knowledge, alcohol and drug use, and sexual risk. Improved HIV prevention efforts are needed to reduce the risk vulnerability of migrants who relocate to high disease prevalence areas.