Additional Study Information: International GBS Outcome Study (IGOS) is a study of the Inflammatory Neuropathy Consortium (INC) and Peripheral Nerve Society (PNS) on disease course and outcome in Guillain-Barr syndrome (GBS). Guillian Barre syndrome is an autoimmune disorder affecting the peripheral nervous system, leading to paralysis and potential fatality if it progresses to involve the respiratory muscles or autonomic nervous system. The IGOS aims to identify various factors which may influence or predict disease course and outcome in individual patients with GBS, as early as possible after onset of disease. The study consists of a prospective observational international multi-centre study including at least 1000 patients with GBS and a follow-up period of at least one year, and all patients within two weeks of onset of weakness can be included. Clinical information will be obtained via a web based data support according to a pre-defined protocol including eight visits: at entry, 1 week, 2 weeks, 4 weeks, 8 weeks, 13 weeks, 26 weeks and 52 weeks. Data collected will include routine diagnostic electrophysiology, serum samples which will include DNA extracted from a single blood sample. There will be an option for patients to participate in two other modules- one to collect during routine diagnostic workup, and another to extend follow up another two or three years. IGOS will result in a large prospective, standardized clinical database and biobank from GBS patients. Expertise Groups will then be able to use this data to determine the processes of disease progression and recovery in GBS, develop prognostic models, conduct selective therapeutic trials, and personalize treatment.