This study investigates some of the mechanisms influence maternal and child healthy by examining the effect of the migration process on the health among the Mexican-origin (Mexican American and Mexican immigrant) population living in South Chicago. Specifically, this study examines the existence of the epidemiological paradox: the empirical finding that health outcomes of infants born to Mexican-born or Mexican- origin or Mexican-origin women are better than the health outcomes of infants born to U.S.-born white women. These health outcomes include low birthweight, pre-maturity, Intrauterine Growth Retardation and survival during the first year. This study first examines the existence of the epidemiological paradox using data collected specifically to address that question, and second, focuses on the less-studied finding of the epidemiological paradox; the result that Mexican immigrants with longer duration in the United States experience a decline in health outcomes. By conducting in-depth interviews, following infant health over time, examining medical records, and analyzing national data on Latinos, this study will provide a longitudinal analysis of prenatal health outcomes of a Mexican population in Chicago.