This study evaluates the acoustic emission (AE) technique for the detection of membrane dehydration in proton exchange membrane fuel cells during operation. The dehydration of the membrane owing to inefficient water management leads to drastic performance losses. Electrochemical impedance spectroscopy (EIS) and AE measurements were carried out during dehydration of Nafion samples. Results have shown that electrochemical parameters obtained from EIS yield monotonic exponential-like responses following the water loss. AE was shown to be sensitive enough to detect structural changes taking place at the last stages of dehydration.