Combined with careful clinical examination, electrophysiology and histopathology have rendered the peripheral nervous system the best studied and most accessible level of the nervous system. But even after intensive diagnostic evaluation of peripheral neuropathies in large diagnostic centers, 24 to 70% of disorders remain unclassified. Analogous statistics for disorders of muscle and neuromuscular transmission are not known but probably similar, if not worse. Clearly, detailed diagnostic characterization of disorders of the peripheral nervous system is the first stage in clinical intervention.