Guillain-Barre syndrome is an acute rapid-onset progressive neurologic disorder over days to 4 weeks. It presents with symmetric weakness often starting in the legs as an ascending paralysis. Reflexes are reduced or absent early in the disease. The condition is immune-mediated by affecting myelin or axons acutely often triggered by preceding infections. There is albuminocytologic dissociation in the cerebrospinal fluid. Electrodiagnosis exhibits acute demyelinating or axonal patterns. The condition must be treated with intravenous immunoglobulin or plasmapheresis and supportive care. There is a good prognosis with treatment.