Foreign aid has been the subject of increasing critique since the 1980s and there has been extensive research on aid effectiveness, particularly focusing on the impact of aid on aggregate economic growth. The scholarly literature remains inconclusive regarding the question of to what extent development aid actually works. One reason for these inconclusive results could be that the large majority of empirical investigations to date have relied on cross-country analyses. As the country-level may be a too highly aggregated unit of analysis to clearly identify effects of development aid, we argue that there is a need for more fine-grained studies. Also, there is a need for studies that address the impact of aid beyond economic growth in the receiving areas. This policy brief summarizes the first systematic attempt to study how development aid affects infant mortality at the subnational level, using the case of Nigeria.