Ion bombardment has been used to modify the interfacial characteristics of diamondlike films produced by using a pulsed arc discharge deposition method. The films were deposited onto annealed unalloyed carbon steel substrates. Two different structures were studied. In the first configuration a 40 nm thick film was deposited directly onto a steel substrate. In the other case a buffer layer of SiC with a thickness of 20 nm was first deposited, followed by a deposition of a 40 nm thick diamondlike film. Both kinds of samples were exposed to ion bombardment of 13C ions at an energy of 50 keV with the fluences of 1015 and 5 × 1015 ions/cm2. Ion bombardment did not result in any changes in the adhesion of the diamondlike film without the buffer layer as determined by using a pull test. However, ion bombardment up to 5 × 1015 ions/cm2 of the sample with the SiC buffer layer improved the adhesion beyond the testing capability of the pull tester. The results are discussed in terms of the thermodynamical properties and computer simulations of the atomic movement at the coating/substrate interface. Preliminary tests on the effect of a high fluence of 1017 ions/cm2 on the adhesion of a diamondlike film on AISI 316 stainless steel were also performed and the results, which are complemented with secondary ion mass spectroscopy (SIMS) measurements, are presented.