Many transmissible spongiform encephalopathies (TSEs) are believed to be caused by a misfolded form of the normal cellular prion protein (PrPC) known as PrPSc. While PrPSc is known to be exceptionally stable and resistant to protease degradation, PrPC has not shown these same unusual characteristics. However, using ion mobility spectrometry mass spectrometry (IMS-MS), we found evidence for at least one very stable conformation of a truncated form of recombinant PrPC consisting of residues 90-231, which resists unfolding in the absence of solvent at high injection energies and at temperatures in excess of 600 K. We also report the first absolute collision cross sections measured for recombinant Syrian hamster prion protein PrP(90-231).