Nanoporous metallic structures formed from dealloying have recently attracted considerable interest due to a wide range of potential applications in areas such as catalysis, actuators, biomedical sensors and fuel cell electrodes. The Cu-Pd system is interesting as a model system for corrosion as well as a potential catalyst material. We report a combined in-situ X-ray diffraction (XRD) and ex-situ atomic force microscopy (AFM) study of the initial structural evolution during the selective dissolution of Cu from Cu3Pd (111) and Cu3Pd (100). The experiments were performed under potential control in 0.1 M H2SO4 solution. Below the critical potential, no distinct diffraction signal is evidenced by in-situ XRD but AFM reveals the existence of islands on the surfaces. At the critical potential, on both single crystal surfaces the formation of an epitaxial Pd layer exhibiting substrate orientation is evidenced by XRD. Ex-situ AFM imaging clearly showed at comparable stages the formation of larger nanoscale islands. We further compare and contrast the behavior of the dealloyed Cu-Pd surfaces with that of Cu-Au alloys. (C) 2013 The Electrochemical Society. All rights reserved.