It has been proposed that the lattice mismatch between a dealloyed layer and the substrate alloy may play a role in the transgranular stress corrosion cracking (TSCC) of copper alloys. This investigation uses the single-exposure X-ray technique to measure the residual stress in a dealloyed layer formed by the selective dissolution of copper (Cu) from a copper-gold (Cu-18Au) alloy. The gold-rich dealloyed layer was found to have an average compressive stress of 39.3 MPa, indicative of a lattice mismatch at the alloy/dealloyed layer interface. Polycrystalline specimens of Cu-18Au that were dealloyed and then stressed during anodic polarization to relatively large overpotentials for copper dissolution showed cracking that propagated well into the substrate alloy. The cracking was predominantly transgranular, and the fracture surfaces showed features consistent with a transgranular cleavage mechanism. On the other hand, specimens that were dealloyed and then stressed while polarized to relatively low overpotentials for copper dissolution, formed cracks in the dealloyed layer that were always arrested at the alloy/dealloyed layer interface. Lateral resolution was a fraction of a micrometre (μm), so that it was obvious that within this resolution limit there was no propagation into the bulk alloy. These results suggest that the lattice mismatch by itself is not sufficient to propagate a crack into the substrate alloy. However, results for a wider range of conditions and with improved resolution are now needed to more completely address this issue.