Guillain-Barré syndrome (GBS) is a recognized entity for which the basis for diagnosis is descriptive in our present state of knowledge. Diagnosis rests upon pattern recognition of the clinical picture plus other features including elevated cerebrospinal fluid protein level, electrophysiological changes of marked slowing of conduction velocities, prolonged distal latencies, dispersion of the evoked responses, and frequent evidence of conduction block, together with pathological changes, when known, of low grade-inflammation and demyelination-remyelination in peripheral nerve. The precise diagnostic limits of GBS remain uncertain.