Guillain-Barré syndrome is the most common paralytic illness affecting children and adolescents in countries with established immunization programs. The term is currently used to encompass a group of disorders in which an autoimmune response occurs days or weeks after an antecedent infection or event (e.g., immunization) and results in an acute polyradiculoneuropathy with flaccid weakness, areflexia, and increased cerebrospinal fluid protein. This chapter reviews the epidemiology, clinical presentation, diagnostic criteria, pathogenesis, treatment, and outcome of this condition.