Immigration is often seen as an instrument of adaptation for ageing countries. In this paper, we evaluate, using a dynamic general equilibrium model, the contribution of migration policy in reducing the tax burden associated with the ageing population in France. Four alternative scenarios, compared with a baseline scenario based on official projections, are simulated with the aim of quantifying the effects of immigration on French social protection finances. We show that the age and, to a lesser extent, the skill structure of immigrants are the key features that mainly determine the effects on social protection finances. Overall, these effects are all the more positive in the short to medium term if the migration policy is selective (in favour of more skilled workers). In the long term, the beneficial effects of a selective policy may disappear. But whatever the degree of selectivity of the migration policy, the financial gains from higher consequent migration flows are relatively moderate compared with the demographic changes implied by ageing.