We presented a case of Guillain-Barré syndrome (GBS) associated with pneumonitis, liver, pancreatic and renal dysfunction, and encephalopathy, who showed an increase in anti-cytomegalovirus (CMV) antibody titer of the serum and cerebrospinal fluid (CSF). A 41-year-old male admitted to our hospital with complaints of gait disturbance and muscle weakness in the extremities. The symptoms appeared following common cold, and developed gradually. Neurological examination showed mild mental symptoms, bilateral abducens, facial and bulbar palsy. Muscle weakness was shown on the neck and four extremities. Bilateral hand tremor, glove and stocking type sensory disturbance, and dysautonomia were also presented. Examination of the CSF revealed albumin-cytologic dissociation, and the anti-CMV antibody titer of the serum and CSF increased significantly. The titer of anti-CMV IgG antibody was 1:6400 in the serum, and was 1:80 in the CSF. Immunological examination showed no immunodeficiency. The conduction velocity of the peripheral motor and sensory nerves was decreased. The coefficient variation (CV%) of the R-R interval was also decreased. P1 and P2 latency and central conduction time for a somatosensory evoked potential (SEP) were also elongated, and paroxysmal abnormality was present on electroencephalogram (EEG). Two days after admission, pneumonitis appeared, leading to respiratory insufficiency. He needed respirator because of bulbar and respiratory disturbance. The chest roentgenogram revealed a consolidation-like shadow in the right upper lung filed. Two weeks after admission, liver, pancreatic and renal dysfunction was noted by biochemical examination of the blood, urinalysis, and abdominal echography. Since 10 days after the onset of GBS, 70 mg/day prednisolone was administered.(ABSTRACT TRUNCATED AT 250 WORDS)