Data from 15 Demographic and Health Surveys are used to examine whether rural-urban migrants in developing countries experience higher child mortality after settling in towns and cities than do lifelong urban residents, and if so, what individual or household characteristics account for this. Findings indicate that children of female migrants from the countryside generally have much poorer survival chances than other urban children. This survival disadvantage is more pronounced in big cities than in smaller urban areas, among migrants who have lived in the city for many years than among recent migrants, and in urban Latin America than in urban North Africa and sub-Saharan Africa. Within big cities, higher child mortality among migrant women is clearly related to their concentration in low-quality housing, and in part to fertility patterns at early ages of children and mother's educational attainment at later ages. Excess child mortality among urban migrants may also result from factors associated with the migration process, that are outlined in this study but not included in the analysis. Evidence of moderately high levels of residential segregation of migrant women in big cities suggests that opportunities exist for urban health programs to direct interventions to this disadvantaged segment of city populations.