The influence of environmental conditions on cubic boron nitride (cBN) film adhesion to silicon substrates was investigated. cBN films were deposited on (100)-oriented silicon substrates by ion-assisted pulsed laser deposition. The irradiating ions were mixtures of nitrogen with (i) argon, (ii) krypton and (iii) xenon. Under room-ambient conditions, the films delaminated in the following time order : N/Xe, N/Kr and N/Ar. cBN films deposited using N/Xe ion-assisted deposition were exposed to four environmental conditions for several weeks : a 1 mTorr vacuum, high humidity, dry oxygen and dry nitrogen. Films exposed to the humid environment delaminated whereas those stored under vacuum or in dry gases did not. Films stored in dry nitrogen were removed after nearly 2 weeks and placed in the high-humidity chamber; these films subsequently delaminated with 14 h. It is concluded that the presence of a humid environment facilitates the delamination of BN thin films from silicon substrates. A model of the interaction between water and the interfacial material is also presented.