With a fall of 42% of Foreign Direct investment (FDI) flows worldwide in 2020, the Covid-19 crisis has raised important concerns about the impact of this source of financing on economic growth in Africa, in particular through its effect on national investment. While FDI is often seen as a welcome boost to economic growth and long run development, its net effect may depend critically on whether it stimulates domestic private investment or crowds it out and over what time horizon. This paper investigates the relationship between FDI and private investment in Sub-Saharan Africa (SSA), using a sample of 40 countries over 1980-2017. To disentangle short term from long-term dynamics, our empirical analysis is based on Pooled Mean Group (PMG), Mean Group (MG) and Dynamic Full Effects (DFE). We find that FDI has little effect on private investment in the short run but significant crowding-in effects in the long-run: a one percentage point increase of the share of FDI in GDP leads to a 0.29% rise in private investment, in the long run. Our results also show that FDI interacts with public domestic investment to boost these positive effects. Finally, we show that the impact of FDI on domestic private investment is stronger in non-natural resource exporting diversified countries as opposed to non-diversified commodity exporters.