The Guillain Barré syndrome is an inflammatory process of the peripheral nervous system. It is potentially reversible. Nowadays it is the commonest cause of acute, generalized, flaccid paralysis in the western world. Our objective was to present the clinical and electrophysiological characteristics of patients with the Guillain Barré syndrome who required admission to an intensive care unit. We therefore report our experience over a period of four years with patients with this syndrome who were admitted to the intensive care unit and given mechanical ventilation. We analyze the current incidence of this syndrome, the proportion of patients requiring admission to the intensive care unit and connection to mechanical ventilators due to their muscle weakness, and the mortality rates of the major case series published. We analyze the electrophysiological findings which indicate worse prognosis. Greater axonal involvement is seen in patients with poorer recovery, whilst those who made a better recovery had a predominantly demyelinating pattern. We studied certain clinical features which implied more severe illness and worse functional recovery such as the appearance of signs of autonomic nervous system involvement, rate of progression until the maximum affectation occurred and advanced age. Finally, we discuss the role of current immunomodulation treatment and the evidence of its effectiveness. The Guillain Barré syndrome patients admitted to the intensive care unit with the greatest index of long term sequelae are characterized by being older, with a higher proportion of neurovegatative disorders and have an electrophysiological pattern showing signs of greater axonal degeneration.