Federal advisory committees are commonplace in the administrative state and often play a critical informational role in policymaking. Public administration scholars have yet to explore fully the implications of the institutional design and intra-committee dynamics that influence the advice produced by advisory committees. Using the Medicare Evidence Development and Coverage Advisory Committee (MEDCAC) as a case, we provide a much needed empirical examination of committee composition, advice, and influence. MEDCAC provides advice to the Centers for Medicare and Medicaid Services (CMS) about what medical treatments to cover under Medicare. Using data from 2005 through 2009, this study compares the voting of different types of committee members and estimates the degree to which CMS coverage decisions correspond to these votes. The results indicate that patient and consumer representatives are generally more optimistic about medical treatments than regular committee members appointed for their expertise, but that these differences are mostly on technical matters. On matters that deal with Medicare benefits more explicitly, and thus come to bear more directly on coverage determinations, the differences in assessments between these representatives and regular committee members are minimal. The results also indicate that the votes of scientific experts correlate with CMS coverage decisions, and they suggest that the votes of guest experts are most influential when there is committee disagreement. Overall, the study yields evidence consistent with the notion that the advice of expert committee members captures the diverse preferences of political stakeholders and that it is influential in CMS’s coverage decisions.