Thin films of hydrogenated amorphous carbon (a-C:H) were prepared from a mixture of 10% methane and 90% hydrogen by the plasma-enhanced chemical vapour deposition (PECVD) technique at an r.f. frequency of 13.56 MHz. Different conditions of pressure, power and gas how rate were employed. The films were characterized by a variety of surface analytical techniques, and ellipsometry was used to characterize the optical properties of the films. The films obtained were uniform, soft, transparent, non-conducting and chemically inert, with good thermal conductivity and high stability. In this paper, we report and discuss some of the parameters that influence the optical properties of the films and the rate at which they are deposited.