Indium tin oxide thin films were deposited at room temperature by RF magnetron sputtering, under different pressures, and annealed in vacuum (10(-6) Torr) in the 473-573 K temperature range. The microstructure of the films was analyzed in order to investigate its dependence on deposition pressure and annealing temperature. A correlation between microstructure and electro-optical properties was also established. Films produced at low pressures are crystalline and have higher conductivity than films deposited at high pressures. Films produced at high pressures are amorphous, but can be crystallized by annealing. With the increase in crystallinity, shifts of the absorption and plasma resonance edges to shorter wavelengths, attributed to an increase in carrier concentration, were observed at the transmittance spectra. (C) 2004 Elsevier Ltd. All rights reserved.