By reducing the cost of care, health insurance positively affects the income of consumers but reduces the returns of investing in prevention that, in turn, affect the risk or severity of illness. This situation in which consumers alter their behavior when provided with health insurance coverage is called moral hazard. After gaining health insurance that covers preventive care, newly insured individuals may increase their consumption of preventive services. However, they may also engage in riskier behaviors. Empirical studies have attempted to test these countervailing effects of insurance coverage in prevention but findings are ambiguous. This dissertation analyzes the impact of Mexico’s Public Health Insurance Program, Seguro Popular (SP) (formally introduced in every Mexican state after the 2003 Mexican health reform to expand coverage to the uninsured), on different measures of healthy behaviors and use of preventive care. Using longitudinal data from the Mexican Life Family Survey (2002-2009), a difference-indifference (DD) approach is used to exploit exogenous variation in SP coverage both across states and over time. Results suggest that SP had positive impact on the use of preventive doctor visits (mostly among women), and on the self-reported use of breast exam among women aged 30-50, but these effects were only temporary. Long-term effects suggest that SP negatively affected the proportion of young women aged 15-29 who report to have a Pap smear periodically, and had a negative impact on the level of physical activity reported by both men and women. Understanding the effect of health insurance on the uptake of preventive care has important policy implications for government sponsored health insurance programs that aim to promote disease prevention and healthy lifestyle choices. Policy options to address these issues include: (i) increased access to preventive services through mobile units of care in remote underserved areas, (ii) gender-specific educational campaigns to provide Mexicans with more and better information about the importance of prevention and services available through SP; and (iii) specific interventions to encourage individuals to take simple steps in their everyday routines that could increase exercise adherence.