Only a few studies have been reported describing polyneuropathies in a series of children. To study the clinical and neurophysiological spectrum of polyneuropathies in a large series of children and obtain an overview of their etiologies, this retrospective study reevaluated all electromyograms and electrophysiologic studies performed between 1995 and 2004 in children under 17 years of age at the Radboud University Nijmegen Medical Center, a tertiary neuromuscular reference center. Electromyograms revealing polyneuropathy were selected for further analysis (n = 118), and the medical records were reviewed to supplement electromyographic findings with the clinical diagnosis. Hereditary polyneuropathies made up 68% of the total, and 54% of these were isolated polyneuropathies; in the remaining 46%, polyneuropathy was part of a more complex disorder. The acquired polyneuropathies were primarily inflammatory. Nerve biopsies had been performed in 22 of the 118 cases (19%) and led to a diagnosis in 4 cases. Despite sophisticated investigation, 11 cases (9%) remained unclassified for underlying cause. Hereditary motor and sensory neuropathies are the most common type of polyneuropathy in childhood, followed by polyneuropathies as part of an inborn error of metabolism and inflammatory polyneuropathies (in patients in whom electromyography was used to diagnose the neuropathy). In the full series of patients, nerve biopsy did not play a prominent role in the diagnostic work-up of childhood polyneuropathies, due to the increasing availability of other laboratory (genetic and metabolic) diagnostic tools. Nerve biopsy nonetheless proved to have an important diagnostic yield in selected, complex cases.