This article uses the 2013 Current Population Survey Annual Social and Economic Supplement to estimate the financial burden of medical out-of-pocket costs by comparing medical out-of-pocket expenditures to income. This measure is important for evaluating the magnitude of burden, better understanding who bears it, and establishing a baseline to assess the impact of the Patient Protection and Affordable Care Act. We examine the distribution of burden and the incidence of high burden across all families and by individuals’ health insurance status and demographic and socioeconomic characteristics. We look more closely at one group vulnerable to having high burden: those younger than age 65 with incomes between 138% and 200% of the federal poverty line. We find that 18.5% of these individuals have incomes below the threshold of expansion Medicaid eligibility after accounting for non-over-the-counter medical expenses and examine the characteristics associated with being classified below this threshold.