Background: Most previous studies comparing the effectiveness of Plasma Exchange (PE) or intravenous immunoglobulin (IVIG) in treating Guillain-Barre syndrome (GBS) have focused on the short-term outcome at around 1 month. Objective: To compare the long-term efficacy of PE and IVIG at one year in adult patients with GBS. Methods: Eighty-one adult patients with acute GBS were randomized into two groups with a ratio of 2 : 1: PE (N = 54) and IVIG (N = 27). Patients were assessed with the Medical Research Council sum score (MRC sum score), GBS Disability Scale (GDS), and Functional assessment of acute inflammatory neuropathy (FAAIN) at baseline, ten days, one month, three months, and one year. Neurophysiological examinations were performed at baseline and three months following treatment. Results: There were no significant differences between groups in demographic, clinical, and laboratory data. Both treatments produced a significant improvement in all clinical rating scales in both groups that continued up to one year. There were significant differences in the time course of recovery in the MRC and FAAIN scales, with significantly more improvement in the IVIG group at 1 and 3 months, although there was no significant difference in outcome at one year. However the effect size showed measurable differences between the PE and IVIG groups across the different measures at one-year. Electrophysiological studies showed equal improvement in most measures in both groups at three months, with a slightly greater effect in the IVIG group. Conclusion: long term outcomes of IVIG and PE were equivalent. However the effect size showed measurable differences between the PE and IVIG groups across the different measures at one-year follow-up that indicate the superiorty of IVIG. There was also a tendency for improvement to be slightly faster in the IVIG group.