Diamond powder and monocrystals were bombarded with 72 MeV carbon ions. The photographs in reflected and transmitted light revealed a layer with a thickness estimated as 7 ±2 μm, where the bombarding ions stopped, as well as a layer with a thickness of about 70 μm, where, due to accidental channelling, some ions had penetrated further into the specimens. The contribution of interstitial atoms to expansion of the diamond crystal lattice was estimated as 1.16±0.30.