The effect of MEA pinhole size on the aging of single (10 x 10 cm(2)) PEMFC was investigated. Two MEAs were perforated by two pins of different diameters (0.7 and 1.2 mm), in both cases in the H-2 inlet zone. The performance losses and the degradation rates of the MEA components were compared to those exhibited by a healthy, not perforated MEA. Perforation by the smaller pin did not promote immediate cell voltage decay and the hydrogen crossover increased only slightly. Perforation by the larger pin resulted in immediate reduction in cell voltage and one decade increase of the hydrogen crossover. LSV and CV voltammograms performed for determination of the crossover and the electrode active surface were changed abruptly by the larger perforation, which confirmed the existence of an internal short circuit within the MEA. Besides, the perforation affected the time variations of the diffusion and charge transfer resistances. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.