By control of phase separation and dewetting of thin blend films of weakly incompatible polymers, particular surface patterns may be generated. These patterns cover a typical height scale from 0.3 nm to 300 nm and most prominent in-plane length scale from 0.1 μm to 100 μm. Characteristic features are holes, regular continuous structures, and drops of these sizes. In addition, conformal rough surfaces with a morphology dominated by one of the underlying substrates can be prepared. The surface morphology was investigated with scanning force microscopy (SFM), while the interface correlation was measured with diffuse X-ray scattering. Both methods together yield a topological description of the examined samples. Observed morphologies originated from phase separation of the thin blend film and from the dewetting of one blend component on top of a continuous film formed by the other component.