Peripheral Myelin Protein-22 (PMP22) is a membrane glycoprotein which represents up to 5% of total protein in myelin of peripheral nerves. Mutations affecting the PMP22 gene have been linked to the inherited peripheral neuropathies Charcot-Marie-Tooth disease type 1A (CMT1A; duplications and point mutations), Dejerine-Sottas syndrome (DSS; point mutations), and hereditary neuropathy with liability to pressure palsies (HNPP; deletions). In this study, we determined the ultrastructural distribution of PMP22 and other myelin proteins in normal human peripheral nervous system (PNS) nerves and in CMT1 patients with or without the CMT1A duplication on chromosome 17. Our results demonstrate that PMP22, P0 protein, and myelin basic protein are present in compact myelin of all patients examined. PMP22 was also present in the plasma membrane of Schwann cells of unmyelinated fibers and onion bulbs. Although the precise biological role of PMP22 remains to be discovered, our results support the hypothesis that this protein serves multiple functions in Schwann cells.