Political parties throughout Latin America rely increasingly on primary elections to select candidates for public office. Where they are adopted, primaries are generally touted as moves toward openness and internal party democracy. Yet politicians and party leaders are concerned with winning elections, and there are reasons to expect that primaries select candidates who are weaker in general election competition than other methods. Using data from every democratic presidential election in Latin America since the late 1970s, we test whether primaries systematically affect candidate strength. We find evidence of a primary bonus—that is, other things equal, primary-selected candidates are stronger than those selected by other procedures.