A 59 year-old-man had ataxia and hemiparesis of progressive onset which resolved in a few weeks. CT scan and magnetic resonance imaging showed white matter multiple lesions. The cerebrospinal fluid was consistent with an inflammatory disease. The diagnosis of multiple sclerosis was evoked. However, the patient had chronic brucellosis and serological rates increased and decreased according to the clinical and radiological signs. Thus, encephalitis caused by brucellosis was evoked. The mechanism is assumed to be a demyelinating process caused by a deep focus reactivation.