This paper reports structural and kinetic information about a two-dimensional phase transition that takes place in the electrochemical study of ethyl viologen on mercury in the presence of iodide ions prior to reduction by diffusion of ethyl viologen dication. Unlike other viologens, it is the dication rather than the cation radical that seemingly forms the condensed phase in this case. (c) 2005 The Electrochemical Society. All rights reserved.