Perfluorosulfonic acid (PFSA) membranes have been used for 40 years as solid electrolytes in low temperature fuel cells and are considered from the scientific community superior to other polymeric products due to their good combination between chemical resistance and proton conductivity. In recent years, development of the class of PFSA membranes known as 'short side chain' membranes has been restarted from Solvay Solexis (Hyflono((R)) Ion). Although PFSA are highly stable, still, decay in fuel cell performance might be detected over time due to membrane degradation, especially under certain working conditions. Different degradation mechanisms, mainly based on Nafion((R)) structure, have been proposed by several Authors and both ex situ and in situ test protocols have been developed to perform accelerated testing. The generally accepted opinion is that the degradation problem is mostly related to peroxide radical attack. A short review of the degradation mechanisms is first presented in this work. For the first time a campaign of chemical degradation tests (open circuit voltage fuel cell operation and ex situ Fenton tests) on the short- side-chain PFSA is presented and discussed, both for standard extruded and chemical stabilized membranes. (C) 2006 Published by Elsevier B.V.