In the framework of the Socio-Economic Research on Fusion (SERF), which was jointly conducted by the European Commission and the Fusion Associations, external costs of future fusion plants were calculated. All the damages that are not reflected in the market price are called external costs. The ExternE methodology was applied. External costs of the fusion power plants are found to be rather low, in the range of a few mEuro/kWh. Radiological impacts are only one source of external effects, but not the dominating one. External costs of fusion compare well with wind and solar energy.