The electrical and optical properties of indium tin oxide (ITO) thin films deposited by plasma ion-assisted evaporation are reported. With deposition at room temperature using certain ion-source parameters ITO films with an electrical resistivity of 5 x 10(-6) Omega m and an absorptance at 550 nm of less than 5% for 300 nm film thickness were obtained. Variation of oxygen pressure during deposition results in different band gap energies and different resistivities. The complex index of refraction was determined using a dispersion model suitable for explaining the particular properties of ITO in the visible and near infrared spectral range.