Guillain Barré syndrome is an acute polyradiculoneuropathy with different forms of presentation and is currently the leading cause of acute arreflexic paralysis in the world, its diagnosis is clinical and additional assesment as electrodiagnosis are used for differential diagnosis, rank among the variants (demyelinating or axonal) and define prognosis. The purpose of this paper is to make a narrative review of the literature, emphasizing the electrophysiological study, describing early findings, the most common mistakes, while highlighting the importance of classification chart to guide actions towards rehabilitation and functional recovery.