The study considers the prediction of the main flow parameters of adiabatic annular two-phase flows, focusing in particular on the void fraction. Recently developed models to predict the entrained liquid fraction, the wall shear stress and the velocity profile in the annular liquid film are discussed and integrated to provide a unified annular flow model that is used to predict the void fraction. A comparison with experimental void fraction data shows that the unified annular flow model slightly outperforms some of the most accurate void fraction empirical correlations currently available.