B diffusion in crystalline Ge is investigated by proton irradiation in thin layers with B delta doping under different fluences (1× 10 15–10× 10 15 H+/cm 2), fluxes (6× 10 11–35× 10 11 H+/cm 2 s), and temperatures of the implanted target (from− 196 to 550 C), both during and after irradiation. B migration is enhanced by several orders of magnitude with respect to equilibrium. Moreover, B diffusion is shown to occur through a point-defect-mediated mechanism, compatible with a kick-out process. The diffusion mechanism is discussed. These results are a key point for a full comprehension of the B diffusion in Ge.