The authors report the case of a patient with severe Guillain-Barré syndrome (tetraplegic and on mechanical ventilation), that was treated with intravenous immunoglobulin (IVIg), 2 g/Kg. At first, there was clinical improvement, followed by clinical deterioration two weeks later. On the second course of IVIg there was, again, clinical improvement and then deterioration, 65 days after treatment. Finally, on the third course of treatment definitive recovery was achieved and no more relapses happened so far (three years after the treatment). The authors review the literature about fluctuations related to treatment with IVIg. Conclusions are that these patients should be closely observed during the first weeks after IVIg treatment, and that further studies are still necessary to elaborate alternative protocols on the prevention of these cases.