We investigated the usefulness of electrodiagnostic (EDX) studies for the early diagnosis of childhood Guillain-Barré syndrome (GBS). We retrospectively reviewed 5 patients (ages, 17-96 months) who fulfilled the diagnostic criteria of GBS. The EDX studies were performed at least twice;they included 1 or more following:motor nerve conduction study (MNCS), F-wave study, electromyography (EMG), and sensory nerve conduction study. The first and second EDX studies were performed at 8 days (range:4-13 days) and 14 days (range: 12-27 days) after the onset of motor symptoms, respectively. Although only 3 of 5 patients showed abnormal findings in the first MNCS, additional EDX studies, namely, F-wave study and EMG confirmed the presence of peripheral neuropathy in all patients. Regarding the classification of GBS subtypes, the results of the first EDX studies lead to the diagnosis of acute inflammatory demyelinating polyneuropathy (AIDP) in 3 patients and the remaining two were diagnosed with AIDP based on results of the second studies. We concluded that serial EDX studies, including F-wave studies, are essential for the early and definite diagnosis of childhood GBS.