Migration during the formative adolescent years can affect important life-course transitions, including the initiation of sexual activity. In this study, we use life history calendar data to investigate the relationship between changes in residence and timing of premarital sexual debut among young people in urban Kenya. By age 18, 64 percent of respondents had initiated premarital sex, and 45 percent had moved at least once between the ages of 12 and 18. Results of the event history analysis show that girls and boys who move during early adolescence experience the earliest onset of sexual activity. For adolescent girls, however, other dimensions of migration provide protective effects, with greater numbers of residential changes and residential changes in the last one to three months associated with later sexual initiation. To support young people's ability to navigate the social, economic, and sexual environments that accompany residential change, researchers and policymakers should consider how various dimensions of migration affect sexual activity.