Exposure of polymer electrolyte fuel cells (PEFCs) to synchrotron radiation (SR) during in situ studies causes irreversible material damage and associated performance losses within minutes. Similar issues may be expected when PEFCs are exposed to X-rays in a micro-X-ray computed tomography (mu-XCT) system. The present work diagnoses the in situ performance and electrochemical active surface area during continuous exposure of a fuel cell in a mu-XCT. After 20 hours of X-ray exposure no degradation was measured. This significant difference can be attributed to the orders of magnitude lower X-ray photon flux during mu-XCT compared to SR. (C) 2016 The Electrochemical Society. All rights reserved.