Objective: To correlate electrophysiologic patterns with sural nerve pathology in children with Guillain-Barre syndrome (GBS). Background: Based on electrophysiologic and pathologic observations, GBS has been divided into demyelinating and axonal subtypes. The acute motor axonal neuropathy (AMAN) involves predominantly motor nerve fibers with a physiologic pattern suggesting axonal damage, whereas the acute inflammatory demyelinating polyneuropathy (AIDP) involves both motor and sensory nerve fibers with a physiologic pattern suggesting demyelination, In this study, we sought to confirm these observations by correlating sural nerve pathology with electrophysiologic findings in GBS patients. Methods: Biopsies of sural nerve from 29 of 50 prospectively studied GBS patients were obtained, Nerves were examined by light and electron microscopy, and with immunocytochemistry for macrophages, lymphocytes, and complement activation products. Results: Sural nerves from AMAN patients were normal or had only a few (0.1% to 0.7%) degenerating fibers without lymphocytic infiltration or complement activation. One patient with reduced sural sensory nerve action potential classified as acute motor sensory axonal neuropathy (AMSAN) had many degenerating fibers (2.3%) in the sural nerve. All three AIDP patients displayed active demyelination, and in two patients, lymphocytic infiltration and complement activation products were observed on the abaxonal Schwann cell surface. Conclusion: Classification of Guillain-Barre syndrome subtypes based on motor conduction studies correlates closely with pathologic changes seen in sural nerve. In acute motor axonal neuropathy cases, the sural nerve is almost completely spared pathologically. In acute inflammatory demyelinating polyneuropathy cases, macrophage-mediated demyelination and lymphocytic infiltration are common in the biopsies of sural nerves.