Objective: In this study, we examined the effect of choice-set size and numeracy levels on a physicianin-training’s ability to choose appropriate Medicare drug plans. Design: Medical students and internal medicine residents (N 100) were randomly assigned to 1 of 3 surveys, differing only in the number of plans to be evaluated (3, 10, and 20). After reviewing information about stand-alone Medicare prescription drug plans, participants answered questions about what plan they would advise 2 hypothetical patients to choose on the basis of a brief summary of the relevant concerns of each patient.Participants also completed an 11-item numeracy scale. Main outcome measure: Ability to answer correctly questions about hypothetical Medicare Part D insurance plans and numeracy levels. Results: Consistent with our hypotheses, increases in choice sets correlated significantly with fewer correct answers, and higher numeracy levels were associated with more correct answers. Hence, our data further highlight the role of numeracy in financial- and health-related decision making, and also raise concerns about physicians’ ability to help patients choose the optimal Part D plan. Conclusion: Our data indicate that even physicians-in-training perform more poorly when choice size is larger, thus raising concerns about the capacity of physicians-in-training to successfully navigate Medicare Part D and help their patients pick the best drug plan. Our results also illustrate the importance of numeracy in evaluating insurance-related information and the need for enhancing numeracy skills among medical students and physicians.