Undocumented migrants from Mexico find themselves in low-paying, high-risk occupations when they move to the United States. They are ineligible for most forms of public assistance and usually do not speak English. Because people who live in poor environments with limited access to resources often suffer from poor health we would expect undocumented migrants to be an unhealthy population. However, Mexicans living in the United States have health profiles equal to or better than middle-class American citizens. Researchers of this epidemiological paradox have suggested that certain aspects of Mexican culture may protect against the negative health outcomes associated with poverty, low levels of education and barriers to the mainstream American health care system. While diet, family support and a few specific health behaviors have been investigated as explanations for the paradox, surprisingly little attention has been paid to Mexican health beliefs and practices. To fill this gap in the literature I conducted an ethnographic study of womens medical knowledge in a Mexican immigrant community in Georgia. In both Mexico and Mexican communities in the United States women are responsible for maintaining the health of their families. Mexican women encourage members of their families to engage in health promoting behaviors, make diagnoses of sick family members and prescribe effective home remedies. The herbal medicines that women bring from Mexico to the United States treat illnesses before they become serious and contribute to good overall health. Mexican women also learn how to navigate the mainstream American health care and social services systems. Finally, women maintain and expand social networks in the United States. The social networks that make undocumented Mexican migration to the United States possible also provide social support and access to information, which are critical for maintaining health.