The relationship between rural to urban migration and child growth and family structure is reported in sample of 302 children from families of low socioeconomic status, living in Guatemala City. The sample was divided into three groups: 1) children of parents born outside the city, 2) children of parents born in the city, and 3) children with one migrant and one city-born parent. Children of migrants to the city were the smallest and significantly shorter than children of migrant city-born parents. Migrant parents also had the largest families; family size correlated negatively with growth in height. Growth in weight followed a pattern similar to height, but no significant differences associated with migration status were found between groups.