This study uses nationally-representative, longitudinal data from Mexico to examine the effect of parental migration on child health. I compare children within households who experience parental migration at different key periods of physical development. This comparison provides an estimate of the migration effect net of those family characteristics that are related both to migration and to child health. Using this type of approach addresses the concern that parents who choose to migrate are selected on a number of key characteristics that also affect child well-being. Results suggest that parental migration negatively affects child height-for-age, a long-term measure of child nutritional status and illness.