Abstract A 69-year-old woman complained of diplopia and truncal titubation after upper respiratory infection. She presented with mydriasis and external opthalmoplegia of bilateral eyes, ataxia, hyporeflexia and cervical-brachial muscle weakness. The protein abnormally increased (49 mg/dl) in the cerebrospinal fluid, and the serum anti-GQ1b and anti-GT1a IgG antibodies were positive. The blood sodium level was 128 mmol/l indicating hyponatremia. She had low plasma osmolarity (251 mOsm/kg), high urine osmolarity (357 mOsm/kg) and high urine sodium level (129 mmol/l), while the blood level of antidiuretic hormone was not able to be measured. She was diagnosed to have Fisher syndrome (FS), pharyngeal-cervical-brachial variant of Guillain-Barre syndrome (PCB) and syndrome of inappropriate secretion of antidiuretic hormone (SIADH). The hyponatremia improved with hyperosmotic saline infusion and restriction of water intake. Intravenous immunoglobulin therapy (IVIg) was effective only for ataxia, but the other symptoms mostly remained unchanged for a month. The serum anti-GQ1b IgG antibody was still positive even after one month. We performed high-dose intravenous steroid-pulse therapy. Then the mydriasis, external opthalmoplegia and cervical-brachial muscle weakness were immediately improved. This was a rare case of FS and PCB complicated with SIADH. IVIg, not steroid therapy, is generally chosen for FS since FS is considered as a variant of Guillain-Barre syndrome and steroid is not effective for Guillain-Barre syndrome as was proven by double-blind study. We suppose that the combined therapy of IVIg and steroid would be effective in patients with complicated symptoms and multiple antibodies.