This article examines the effect of insurance coverage on mental health outcomes by exploiting variation in the timing of Medicaid expansion under the Affordable Care Act (ACA). Using BRFSS data from 2007 to 2013, we compare self-reported mental and physical health between individuals in seven states that enacted more generous Medicaid eligibility guidelines before the federal deadline set in the ACA with individuals in variously defined control groups. Results show that while Medicaid expansion improves mental health, it does not have a statistically significant effect on physical health in the short-run. Furthermore, the benefits of Medicaid expansion on mental health status are evident between the passage of ACA in 2010 and the actual implementation of Medicaid expansion. This suggests that insurance coverage may improve mental health status by relieving the stress associated with being uncovered.