Amorphous hydrogenated carbon-nitrogen films, a-C(N):H, were deposited by plasma enhanced chemical vapor deposition using acetylene-nitrogen mixtures. Film composition and density were determined by means of ion beam techniques being the him microstructure studied by infrared and Raman spectroscopies. Films were obtained with nitrogen content up to 22 at. %. As for films obtained using other gas mixtures, the deposition rate showed a strong decrease upon nitrogen incorporation, although with a smaller rate. The film growth kinetic is discussed and some specific features of acetylene-nitrogen precursor gas mixtures are pointed out. A remarkable decrease on the C atom sp(3) fraction was inferred for nitrogen contents higher than 10 at. %, and was correlated to the film density behavior. The mechanical hardness and internal stress were relatively insensitive to low nitrogen incorporation, with a systematic decreasing behavior for nitrogen contents above 10 at. %.