Objectives: In this article, the authors investigate the association between age at migration and mortality during a 13-year period in a sample of Mexican American immigrants aged 65 and older at baseline. Methods: The authors use the Hispanic Established Populations for Epidemiologic Studies of the Elderly (H-EPESE) to control for mortality-related health and social factors. Results: Analyses show that the immigrant generation does not represent a homogeneous mortality risk category. Individuals who migrated to the United States in mature adulthood have a considerably lower risk of death than individuals who migrated in childhood or midlife. Chronic conditions or functional capacity do not account for these differences. Conclusion: Findings suggest that standard risk pools may differ significantly on the basis of genetic and unmeasured life-course factors. A better understanding of the late life immigrant mortality advantage has important implications for more effective and targeted social and medical interventions.