Acute disseminated encephalomyelitis (ADEM) and Guillain-Barré Syndrome (GBS) are commonly recognized as separated entities involving different parts of the nervous system. However, they share some features such as: autoimmune pathogenesis, myelin injury and previous history of viral infections or vaccination. We report the case of a 41 year-old man who developed fever, lower limbs weakness and obtundation fifteen days after an acute gastroenteritis. Neurological examination showed patellar hypereflexia, bilateral Babinski and neurogenic bladder. Twenty-four hours later he developed flaccid paraparesis, generalized areflexia and respiratory failure that was supported by mechanical ventilation. Cerebrospinal fluid showed mononuclear pleocytosis and elevated proteins. Electrodiagnosis showed important reduction of conduction velocity on both peroneal nerves. Magnetic Resonance Imaging revealed white matter lesions in brain, pons and thoracic levels of the spinal cord. Diagnosis of the association between ADEM and GBS (ASADEM-GBS) was made and treatment with corticosteroids and intravenous immunoglobulin was started. The patient recovered motor, sensory and bladder functions and he was able to walk six months later. ASADEM-GBS is an uncommon entity generally considered of poor outcome; however a rapid diagnosis and treatment can substantially improve the prognosis.