Guillain–Barré syndrome (GBS) (French pronunciation: [ɡiˈlɛ̃ baˈʁe], English pronunciation: /ˈɡiːlænˈbɑreɪ/), sometimes Landry's paralysis or Guillain–Barré-Strohl syndrome, is an acute polyneuropathy, a disorder affecting the peripheral nervous system. Ascending paralysis, weakness beginning in the feet and hands and migrating towards the trunk, is the most typical symptom, and some subtypes cause change in sensation or pain as well as dysfunction of the autonomic nervous system. It can cause life-threatening complications, in particular if the breathing muscles are affected or if there is autonomic nervous system involvement. The disease is usually triggered by an infection.

The diagnosis is usually made by nerve conduction studies and with studies of the cerebrospinal fluid. With prompt treatment by intravenous immunoglobulins or plasmapheresis, together with supportive care, the majority will recover completely. Guillain–Barré syndrome is rare, at 1–2 cases per 100,000 people annually, but is the most common cause of acute non-trauma-related paralysis in the world. The syndrome is named after the French physicians Georges Guillain and Jean Alexandre Barré, who described it in 1916.