The Hispanic population in the United States continues to expand rapidly due primarily to a large flow of immigrants from Mexico. Historical observations of disadvantage in the immigrant population, when compared to the native population, had helped to shape prevailing theories on immigration and mental health. However, data emerging from new research on Mexican Americans have come to challenge the old idea that immigrants are necessarily disadvantaged. The goal of this article is to review these new studies critically, to draw conclusions concerning the relationship between immigration and psychopathology, and to offer potential explanations for the major findings. We review five recent large-scale studies that examined the prevalence of mental disorders among Mexican-born immigrants and U.S.-born Mexican Americans in the United States. Results of these studies are inconsistent with traditional tenets on the relationship among immigration, acculturation, and psychopathology. They show that Mexico-born immigrants, despite significant socioeconomic disadvantages, have better mental health profiles than do U.S.-born Mexican Americans. Possible explanations for the better mental health profile of Mexican immigrants include research artifacts such as selection bias, a protective effect of traditional family networks, and a lower set of expectations about what constitutes "success" in America. The elevated rates of psychopathology in U.S.-born Mexican Americans may be related to easier access to abused substances and an elevated frequency of substance abuse among the U.S.-born.