Patients who develop Guillain-Barré syndrome (GBS) face an uncertain future. Although GBS is a well-studied neuro-immunological disease, the disease course and clinical outcome is still not easily predictable for the individual patient. Ranging from mild tingling in feet and hands to a peripheral locked-in syndrome with complete tetraplegia, ophthalmoplegia and respiratory insufficiency needing ventilator support, GBS remains a challenging disease for both patients and treating physicians. The cause of this heterogeneity is for the most part still unknown which impedes the development of novel treatments and personalized medicine. The aim of the study in this thesis was to gain insight into the diversity of the phenotype of GBS and to describe the variety of the current treatment practice of GBS. These studies were largely based on an international, observational cohort study; the International GBS Outcome Study (IGOS).The first part describes the clinical variety and variant forms in the IGOS cohort, and investigates regional variation of GBS. The second part focusses on treatment dilemmas including treatment of patients who have a predicted poor prognosis and patients with a mild form of GBS.