Silicon dioxide thin films for optical applications were prepared by both conventional and ion-assisted evaporation. The residual stresses were determined in air and in vacuum by measurements of the radius of curvature of silicon substrates. The optical properties of the films were deduced from spectrophotometric measurements. The density of the films was deduced from Rutherford backscattering analyses. The optical properties, density and residual stresses were investigated as a function of the ion current and ion energy. Two types of stress, namely intrinsic and water-induced stresses, can be distinguished. The origins of these two components were elucidated and discussed. The stress level was correlated with the film density. The results are compared with those previously obtained for SiO2 thin films prepared by conventional evaporation.