We have studied the effect of the surface and interface on the phase separation of thin films of a blend of deuterated polystyrene and poly(alpha-methyl styrene) using He-3 nuclear reaction analysis. In the unstable region of the phase diagram, surface directed spinodal decomposition is observed. We describe the growth of the morphology and see that the depletion layer behind the wetting layer at the substrate grows faster than the wetting layer at the vacuum interface with power law growth exponents of 0.27 and 0.14, respectively. The early size of the wetting layer is compared with a theoretical zero-time spinodal wavelength. This wavelength decreases when the film is thinner than a critical thickness in accord with other workers.