A case of aseptic meningoencephalitis with recurrent abnormal behavior, status epilepticus and aphthous stomatitis was described. A 39-year-old man, who had a history of low grade fever and abnormal behavior over 2 years without mucocutaneo-ocular symptoms, was admitted to Shinshu University Hospital because of status epilepticus. On admission, neurological examination revealed comatose state with neck stiffness, anisocoria (right greater than left), conjugate deviation to right and bilateral pyramidal tract signs. His cerebrospinal fluid examination revealed a total protein content of 206 mg/dl with 22 lymphocytes and 134 polymorphonuclear leukocytes/mm3. EEG recorded on the 3rd hospital day showed periodic sharp waves and polyspikes, occurring every 1 seconds, predominantly arise from the right hemisphere, which corresponds to periodic lateralized epileptiform discharges (PLEDs). Herpes simplex encephalitis was suspected and acyclovir was administered. Neck stiffness and cerebrospinal fluid findings were improved and PLEDs disappeared. But aphthous stomatitis appeared and meningoencephalitis was relapsed. Laboratory examination revealed erythrocyte sedimentation rate 40 mm/hr, positive C-reactive protein, elevated CH50 and sialic acid, enhanced migration of neutrophils and HLA-B 51. Neuro-Behçet's syndrome was strongly suspected with laboratory data but the clinical course was atypical. His clinical signs were markedly improved after administration of prednisolone. The present case suggests that neuro-Behçet's syndrome with only a part of major symptoms could be diagnosed as viral encephalitis and acyclovir may be effective for the treatment of neuro-Behçet's syndrome.