This paper investigates the effect of foreign direct investment (FDI) on economic growth conditional on the institutional quality of host countries. We first develop several theoretical arguments to show that institutional heterogeneity may be an explanation for the mixed results of previous empirical studies. Second, using a panel smooth regression model on a large sample of developing countries, we show that FDI has a positive effect on growth only beyond a certain threshold of institutional quality. To benefit from FDI‐led growth, institutional reforms should thus precede FDI attraction policies. Additionally, some reforms seem to promote faster marginal effects of FDI, while institutional complementarities may lead to an incremental effect on growth.