Inherited polyneuropathies present in the first 2 years of life are discussed with emphasis on clinical, pathologic, and molecular data. Early-onset polyneuropathies are relatively rare, sometimes life-threatening conditions that demand early recognition by clinical and pathologic examination. Histologic and ultrastructural overlaps among the various conditions are sometimes resolved by molecular genetic analysis. The growth in disease identification by genetic localization allows a more comprehensive understanding of the clinical and morphologic heterogeneity involving rearrangements of the same gene. Molecular mechanisms explaining the acquisition of such gene rearrangements are beginning to be unraveled. Peripheral myelin disorders may be confused with primary axonal disorders, and electrophysiologic examination often helps to distinguish between these two. Furthermore, early-onset central nervous system disorders may present as peripheral polyneuropathies and confound the clinical picture. A tentative diagnosis can often be offered by pathologic examination and confirmed by biochemical enzyme analysis later. The differential clinical diagnostic considerations of early-onset polyneuropathies are offered, to help clinicians sort out these diseases in the most efficient manner.