Lecture outline The peripheral neuropathy, GBS, is the most common form of acute neuromuscular paralysis (annual incidence ~1-2 per 100,000). Most GBS cases follow a trivial bacterial or viral infection, suggesting a post-infectious autoimmune mechanism for disease. Autoimmunity to gangliosides is thought in part to underlie the disorder, although antibodies are detectable by current methods in only about half of the patients, predominantly those with axonal forms. GBS is characterized by muscle weakness, peaking at ~4 weeks from onset, areflexia and variable sensory disturbance. Although most patients recover, there is ~5-10% mortality or long-term morbidity. Distinct variants can be discriminated within the spectrum of clinical, serological and electrodiagnostic characteristics. Acute inflammatory demyelinating polyneuropathy (AIDP), the most common variant in the Western world, is hallmarked by demyelination, mostly without axonal damage. In other forms axonal degeneration occurs specifically in motor axons (acute motor axonal neuropathy, AMAN) or in both motor and sensory axons (acute motor and sensory axonal neuropathy, AMSAN). Recently, intermediate phenotypes have been defined. This talk will review clinical studies on pathogenesis and treatment of GBS, underpinned by more basic data derived from experimental studies.