The influence of preparation conditions on the structure and optical properties of cadmium selenide (CdSe) thin films deposited by thermal evaporation under vacuum onto glass substrates was studied. The structural investigations performed by means of X-ray diffraction (XRD) technique, scanning electron microscopy (SEM) and atomic force microscopy (AFM), showed that the films have a polycrystalline and hexagonal (wurtzite) structure. Transmission spectra, in the spectral domain 600-1400 nm, are investigated. The values of some important parameters of the studied films (absorption coefficient, optical bandgap energy and refractive index) are determined from these spectra. The values of the energy gap, E-g (allowed direct transitions), calculated from the absorption spectra, ranged between 1.65 and 1.75 eV. (C) 2003 Elsevier Science B.V. All rights reserved.