Although its involvement in prion replication and neurotoxicity during transmissible spongiform encephalopathies is undisputed, the physiological role of the cellular prion protein (PrPC) remains enigmatic. A plethora of functions have been ascribed to PrPC based on phenotypes of Prnp−/− mice. However, all currently available Prnp−/− lines were generated in embryonic stem cells from the 129 strain of the laboratory mouse and mostly crossed to non-129 strains. Therefore, Prnp-linked loci polymorphic between 129 and the backcrossing strain resulted in systematic genetic confounders and led to erroneous conclusions. We used TALEN-mediated genome editing in fertilized mouse oocytes to create the Zurich-3 (ZH3) Prnp-ablated allele on a pure C57BL/6J genetic background. Genomic, transcriptional, and phenotypic characterization of PrnpZH3/ZH3 mice failed to identify phenotypes previously described in non–co-isogenic Prnp−/− mice. However, aged PrnpZH3/ZH3 mice developed a chronic demyelinating peripheral neuropathy, confirming the crucial involvement of PrPC in peripheral myelin maintenance. This new line represents a rigorous genetic resource for studying the role of PrPC in physiology and disease.