Decentralization reform has both advantages and risks. Bringing service delivery ‘closer to the people’ can improve information flows and strengthen accountability, but it may also leave systems vulnerable to elite capture and corruption by municipal government officials. While past research has acknowledged the possibility of corruption under decentralization, relatively little work has connected those risks to features of these reforms or specific local institutional arrangements. To explore the conditions that can help mitigate the risks of corruption under decentralization, we study the case of health sector reform in Honduras where municipal governments, associations, and NGOs each serve as intermediary managing organizations under a common decentralized health service delivery model. We argue that three types of institutional arrangements reflecting local accountability practices serve as checks on the authority granted through decentralization and can help guard against corruption: external supervision, civil society engagement, and public participation. Empirically, we draw on data from more than 600 street-level bureaucrats, valuable but under-utilized informants about municipal corruption, across a matched sample of 65 municipalities with contrasting forms of administration. We find that reported corruption is highest under decentralization led by municipal governments, as compared to association- or NGO-led varieties. Both external supervision and civil society engagement help attenuate the positive association between decentralization and corruption, but public participation does not. Overall, this research highlights the importance of considering reform features and local conditions when designing policies to help manage risks and support effective social sector decentralization.