The Affordable Care Act was intended to address systematic health inequalities for millions of Americans who lacked health insurance. Expansion of Medicaid was a key component of the legislation, as it was expected to provide coverage to low-income individuals, a population at greater risk for disparities in access to the health care system and in health outcomes. Several studies suggest that expansion of Medicaid can reduce insurance-related disparities, creating optimism surrounding the potential impact of the Affordable Care Act on the health of the poor. However, several impediments to the implementation of Medicaid's expansion and inadequacies within the Medicaid program itself will lessen its initial impact. In particular, the Supreme Court's decision to void the Affordable Care Act's mandate requiring all states to accept the Medicaid expansion allowed half of the states to forego coverage expansion, leaving millions of low-income individuals without insurance. Moreover, relative to many private plans, Medicaid is an imperfect program suffering from lower reimbursement rates, fewer covered services, and incomplete acceptance by preventive and specialty care providers. These constraints will reduce the potential impact of the expansion for patients with respiratory and sleep conditions or critical illness. Despite its imperfections, the more than 10 million low-income individuals who gain insurance as a result of Medicaid expansion will likely have increased access to health care, reduced out-of-pocket health care spending, and ultimately improvements in their overall health.