We have used laser confocal fluorescent microscopy and atomic force microscopy to study surface and bulk morphologies in solvent cast poly(methyl methacrylate) (PMMA)/polystyrene (PS) films. The solvent evaporation rate strongly affects the surface morphology. Sufficient suppression of solvent evaporation results in a periodic distribution of highly monodisperse PMMA-rich domains. Formation of the surface pattern is interpreted in terms of diffusion-driven coarsening of the minor phase and flow induced by the diffusive transport of PMMA molecules from the bulk of the liquid film to the air-film interface.