We investigate the stress evolution in situ during the potentiostatic electrodeposition of metastable, nanostructured Au-Ni alloy films and develop a correlation between alloy composition, deposition rate, growth mode, and the observed stress state. We find that the internal stresses during Au-Ni deposition can be explained, at least for Ni-rich films, assuming a three-dimensional Volmer-Weber growth mode, where the stress is initially compressive, then transitions to tension, and finally remains tensile over longer times. The observed trends in maximum compressive stress, compressive-to-tensile transition thickness, and net steady-state tensile stress (SSTS) with alloy composition can all be related to the observed decrease in grain size with increasing Ni content. In particular, the SSTS is hypothesized to be the result of a dynamic competition between the stresses generated from nanoscale roughening and adatom insertion into grain boundaries. The Au-rich films, however, do not follow the above trends, suggesting that other stress mechanisms may be operative in this compositional range. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3477933] All rights reserved.