This study analyzed 369 Guillain-Barré syndrome (GBS) patients enrolled in a trial comparing plasma exchange, intravenous immunoglobulin, and combined treatments. Patients were classified into five electrophysiological groups: 69% demyelinating, 3% axonal, 3% inexcitable, 2% normal, and 23% equivocal. Axonal patients were more likely to have a preceding diarrheal illness than others. Antiganglioside GM1 antibodies were more common in axonal and inexcitable groups. Patients with inexcitable nerves had a worse outcome (50% unable to walk unaided at 48 weeks) compared to others (15%). Pure motor GBS patients (16% of all patients) had normal sensory examination and action potentials, were more likely to have preceding diarrhea and antiganglioside GM1 antibodies, but had similar outcomes. Axonal patients were more likely to have normal sensory action potentials. Outcomes did not differ significantly between treatment groups or neurophysiological categories. The study highlights the importance of electrophysiological classification in understanding GBS subtypes and their clinical associations. Patients with axonal GBS were more likely to have preceding diarrheal illness and antiganglioside GM1 antibodies. Pure motor GBS patients had similar outcomes to other GBS patients. The study also shows that electrophysiological criteria for demyelination can vary, and that the Dutch criteria were similar to the authors' criteria. Antiganglioside GM1 antibodies were more common in axonal and inexcitable groups. The study concludes that electrophysiological classification is important for understanding GBS subtypes and their clinical associations. Patients with axonal GBS had a worse prognosis than those with demyelinating GBS. The study also shows that the prognosis of GBS can change over time, with some patients initially classified as axonal later being classified as demyelinating. The study emphasizes the importance of electrophysiological classification in understanding GBS subtypes and their clinical associations.This study analyzed 369 Guillain-Barré syndrome (GBS) patients enrolled in a trial comparing plasma exchange, intravenous immunoglobulin, and combined treatments. Patients were classified into five electrophysiological groups: 69% demyelinating, 3% axonal, 3% inexcitable, 2% normal, and 23% equivocal. Axonal patients were more likely to have a preceding diarrheal illness than others. Antiganglioside GM1 antibodies were more common in axonal and inexcitable groups. Patients with inexcitable nerves had a worse outcome (50% unable to walk unaided at 48 weeks) compared to others (15%). Pure motor GBS patients (16% of all patients) had normal sensory examination and action potentials, were more likely to have preceding diarrhea and antiganglioside GM1 antibodies, but had similar outcomes. Axonal patients were more likely to have normal sensory action potentials. Outcomes did not differ significantly between treatment groups or neurophysiological categories. The study highlights the importance of electrophysiological classification in understanding GBS subtypes and their clinical associations. Patients with axonal GBS were more likely to have preceding diarrheal illness and antiganglioside GM1 antibodies. Pure motor GBS patients had similar outcomes to other GBS patients. The study also shows that electrophysiological criteria for demyelination can vary, and that the Dutch criteria were similar to the authors' criteria. Antiganglioside GM1 antibodies were more common in axonal and inexcitable groups. The study concludes that electrophysiological classification is important for understanding GBS subtypes and their clinical associations. Patients with axonal GBS had a worse prognosis than those with demyelinating GBS. The study also shows that the prognosis of GBS can change over time, with some patients initially classified as axonal later being classified as demyelinating. The study emphasizes the importance of electrophysiological classification in understanding GBS subtypes and their clinical associations.