Objective To investigate the determinants and quality of coverage decisions among uninsured choosing plans in a hypothetical health insurance marketplace. Study Setting Two samples of uninsured individuals: one from an Internet‐based sample comprised largely of young, healthy, tech‐savvy individuals (n = 276), and the other from low‐income, rural Virginians (n = 161). Study Design We assessed whether health insurance comprehension, numeracy, choice consistency, and the number of plan choices were associated with participants' ability to choose a cost‐minimizing plan, given their expected health care needs (defined as choosing a plan costing no more than $500 in excess of the total estimated annual costs of the cheapest plan available). Data Collection Primary data were collected using an online questionnaire. Principal Findings Uninsured who were more numerate showed higher health insurance comprehension; those with more health insurance comprehension made choices of health insurance plans more consistent with their stated preferences; and those who made choices more concordant with their stated preferences were less likely to choose a plan that cost more than $500 in excess of the cheapest plan available. Conclusions Increasing health insurance comprehension and designing exchanges to facilitate plan comparison will be critical to ensuring the success of health insurance marketplaces.