Few cases of simultaneous acute demyelination of the peripheral and central nervous systems are reported. Four patients diagnosed as having Guillain-Barré syndrome and acute disseminated encephalomyelitis during the same hospitalization are described herein. Two patients manifest an atypical form of Guillain-Barré syndrome, with magnetic resonance imaging of the head showing acute disseminated encephalomyelitis. A third patient has acute disseminated encephalomyelitis and develops Guillain-Barré syndrome during his hospitalization. A fourth patient demonstrates transverse myelitis that evolves into Guillain-Barré syndrome, with demyelination seen on brain magnetic resonance imaging. All patients are treated with intravenous immunoglobulins or corticosteroids. Three patients have a favorable outcome; 1 patient has a chronic inflammatory demyelinating polyradiculoneuropathy. Guillain-Barré syndrome and acute disseminated encephalomyelitis can occur simultaneously in the pediatric population. This may be explained by a shared epitope between peripheral and central nervous system myelin. Further research is necessary to better describe this entity and its prognosis.