A new experimental apparatus has been set up to analyze the polymer dilation as well as the stress profile induced by vapor sorption in constrained films. The device couples the bending cantilever technique with a new digital micrometer, which allows one to measure both deflection and polymer swelling at the same time. The apparatus has been applied to study the effects of acetonitrile mass uptake in polycarbonate at 40 degrees C, obtaining the time evolution of swelling and of cantilever deflection during integral sorption tests, in the activity range from 0 up to 0.35. A simulation model is also proposed, which couples Fick's law for diffusion to the study of strain and stress distributions in the cantilever; the mechanical problem has been formulated following the classical laminate theory. The relevant values of the material properties entering the model, such as solubility, diffusivity, and penetrant induced dilation, have all been determined through separate independent measurements, and the results obtained are in good agreement with the corresponding values reported in the literature. The simulation model is able to predict with good precision both the kinetics of 14 deflection during sorption and its final equilibrium value, as well as the overall swelling kinetics, with no need of any adjustable parameters. The model also allows one to calculate the time evolution of the stress 14 profile in the polymer film during sorption/desorption steps.