We review some recent simulation results on mechanisms of damage production close to a surface during ion irradiation. The simulation work encompasses studies of several metals and semiconductors at irradiation energies ranging from a few tens of eVs to 50 keV. The results show that in dense metals the presence of a surface can dramatically enhance the damage production upto energies of at least 50 keV. The added damage is mostly in the form of vacancy clusters, which can extend quite deep, ∼10 nm, in the sample. In semiconductors, by contrast, the surface in general has little effect on the damage production in bulk.