Reported herein is an adult case of Fisher syndrome (FS) that occurred as a complication during the course of community-acquired pneumonia caused by Mycoplasma pneumoniae. A 38-yr-old man who had been treated with antibiotics for serologically proven M. pneumoniae pneumonia presented with a sudden onset of diplopia, ataxic gait, and areflexia. A thorough evaluation including brain imaging, cerebrospinal fluid examination, a nerve conduction study, and detection of serum anti-ganglioside GQ1b antibody titers led to the diagnosis of FS. Antibiotic treatment of the underlying M. pneumoniae pneumonia was maintained without additional immunomodulatory agents. A complete and spontaneous resolution of neurologic abnormalities was observed within 1 month, accompanied by resolution of lung lesions.