Ion-beam-induced deposition (IBID) is a powerful technique for prototyping three-dimensional nanostructures. To study its capability for this purpose, the authors investigate the proximity effect in IBID of nanopillars. In particular, the changes in shape and dimension of pillars are studied when a second pillar is grown near an existing pillar. On a semiconducting bulk Si and on an insulating Si3N4 membrane the first pillar gets broader, whereas on Si it starts to bend. They attribute the broadening and bending to the additional deposition induced by the particles scattered from the growing second pillar. On Si the second pillar is taller than the first one, while on Si3N4 it is shorter and rougher. This difference points to an important role of the substrate conductivity in the proximity effect. In a conductive environment the changes in the second pillar are mainly caused by a precursor coverage enhancement in the pillar surface. This enhancement is caused by precursor molecules, which are reflected or desorbed from the first pillar. In the case of an insulating environment, the changes in the second pillar are mainly caused by the reduction in the substrate surface charging due to the presence of the first pillar.