In the 1980s and 1990s, single-disease interest groups emerged as an influential force in U.S. politics. This article explores their effects on federal medical research priority-setting. Previous studies of advocacy organizations’ political effects focused narrowly on direct benefits for constituents. Using data on 53 diseases over 19 years, I find that in addition to securing direct benefits, advocacy organizations have aggregate effects and can systemically change the culture of policy arenas. Disease advocacy reshaped funding distributions, changed the perceived beneficiaries of policies, promoted metrics for commensuration, and made cultural categories of worth increasingly relevant to policymaking.