A coupled two-phase shear layer/liquid film calculation method is presented for the prediction of the simultaneous motion of a wavy liquid film and the two-phase stream flowing above it. Conservation equations, for both the shear layer and the liquid film, are cast in a compatible integral form and solved together through a space-marching technique. The system of equations resulting for both streams is enhanced through a set of semi-empirical models, appropriately modified to match the proposed method, in order to effect closure. These models deal with various physical aspects including (a) velocity profiles within the liquid film, (b) the structure of the interface and (c) any exchange of information between the two streams. Evaluation of the method is performed in cases where liquid films are developed along flat surfaces, for which measurements and/or numerical results are available.