What accounts for the surge in the electoral success of populist movements in Latin America and the Caribbean (LAC) in the last twenty-five years? This paper argues 1.) that patronage-based political systems are more susceptible than programmatic systems to appeals from populist outsiders, and 2.) that decentralized patronage-based party systems are more susceptible than centralized ones. This argument is tested against evidence on the electoral fortunes of populists in LAC from 1981 to 2012. Decentralization is a robust predictor of populist success in patronage democracies, whether measured in terms of electoral victory or vote share. In addition, contrary to expectations derived from much case study research, populist success is associated with economic growth, not decline. An instrumental variables analysis to control for the potential endogeneity of decentralization to party system instability provides support for the main empirical analysis.