ObjectiveTo explore the characteristics of electrodiagnostic abnormalities at early stage of Guillain-Barré syndrome, and to determine which is the common most frequent and sensitive nerve conduction pattern. MethodsWe retrospectively reviewed the neurophysiological studies of all patients with Guillain-Barré Syndrome discharged from S. Anna Hospital in Ferrara, Italy from 2001 to 2007. Results26 patients (81%) had abnormal F wave. 11 patients (34%) had low amplitude or absent SAPs. 13 patients (41%) reduced compound muscle action potential, slowed conduction velocity, prolonged distal latency and conduction block were more fewer (respectively 12.5%, 25% and 6%). Only in 1 patient we had normal findings. ConclusionF wave is more sensitive than nerve conduction study at early stage of Guillain-Barré Syndrome. Abnormalities of F wave (frequency reduced, prolonged latency) are the most frequent and earlier test for Guillain-Barré Syndrome.