Deposition of cubic boron nitride in hydrogen plasma is thought to proceed as a result of selective etching of sp(2)-hybridized boron nitride from the surface of the growing boron nitride film, the impact of hydrogen atoms or ions leading to formation of c-BN sp(3) bonds on the surface and formation of metastable BNHx species in the gas phase. The mechanism of nucleation and growth of c-BN crystals in hydrogen plasmas is proposed.