The commercialization of polymer electrolyte membrane fuel cells has been hindered by durability problems caused by defects in the manufacturing process. We demonstrate for the first time a non-destructive, non-contact method that uses optical microscopy and image analysis to identify defects that may lead to failure in catalyst-coated membranes (CCMs) of polymer electrolyte membrane fuel cells. This method is applied to 2 commercial CCMs produced by the decal transfer technique. Defects in the catalyst layer (CL) at the beginning-of-life (BOL) are characterized in terms of their initial size and shape, and their propagation is tracked as the CCMs are aged in a non-reactive environment. The defected area in one of the commercial CCMs increases from approximately 2.4% of the total CL area at BOL to 10.5% by end-of-life (EOL). BOL defects in the CL are found to propagate faster in the CCMs stored for 2years under atmospheric conditions compared with freshly manufactured CCMs with narrow CL defects. Image analysis of another commercial CCM shows the presence of pores with diameters between 5 and 25m that comprise 52% of the total pore area in the CL. Other defects such as scratches and missing/empty catalyst areas are identified and characterized, providing a framework for quality control applications. Finally, the effect of defects on fuel cell performance is characterized by measurement of the open-circuit voltage (OCV). These experiments show that CCMs with a large number of cracks in the CL exhibit a voltage loss of 2.55mV/hr, whereas CCMs with thin/missing/empty CL defects show a loss of 1.12mV/hr.