This study analyzed the retirement behavior of Mexicans with migration spells to the United States that returned to Mexico and non-migrants. The analysis is based on rich panel data from the Mexican Health and Aging Study (MHAS). Approximately 9 percent of MHAS respondents age 50 and older reported having lived or worked in the United States. These return migrants were more likely to be working at older ages than non-migrants. Consistent with much of the prior research on retirement in the United States and other developed countries, Mexican non-migrants and return migrants were responsive to institutional incentives. Both groups were more likely to retire if they had publicly provided health insurance and pensions. In addition, receipt of U.S. Social Security benefits increased retirement rates among return migrants. Return migrants were more likely to report being in poor health and this also increased the likelihood of retiring. The 2004 draft of an Agreement on Social Security would coordinate benefits across United States and Mexico boundaries to protect the benefits of persons who have worked in foreign countries. The agreement would likely increase the number of authorized and unauthorized Mexican workers and family member eligible for Social Security benefits. The responsiveness of current, older Mexican return migrants to pension benefits, suggests that an agreement would affect the retirement behavior of Mexican migrants.