Postmortem thickness and morphology studies on a degraded membrane electrode assembly (MEA) caused by carbon corrosion under a local H2 starvation operation in a proton exchange membrane (PEM) fuel cell were carried out using optical, scanning, and transmission electron microscopy. Samples used for the postmortem studies were selected and indexed with the aid of a limiting current density distribution map that was premeasured from the degraded MEA using an electrochemical diagnostic technique. An explicit correlation was found between the postmortem studies and the diagnostics: where the electrode structure damage (i.e., thickness reduction and porosity collapse) is significant, the limiting current density is low. The structure damage and current density drop were found to be in the H2 -starved region where the carbon corrosion is severe. The results presented here are of significance in understanding the fundamentals of carbon corrosion mechanism and related structural origin of fuel cell performance degradation.