A 81 year-old female, weighing 56 kgs, had taken carbamazepine (10.2 mg/kg/day) for simple partial motor seizures of recent onset during 15 days. EEG recording showed slow waves on the left hemisphere. CT was normal. The seizures were controlled for a few days and then reappeared beginning as simple partial seizures and progressing to impairment of consciousness. The patient became confused. On admission she was severely confused. Neurological examination was otherwise normal. Plasma sodium level was 134 meq/l and CBZ plasma level was 4.3 micrograms/ml. EEG showed high voltage bilateral delta waves and a left focus. The drug was withdrawn with relief of clinical symptoms and to a lesser extent, of EEG abnormalities. Phenytoin encephalopathy is a well known pathological entity but to our knowledge there has been no report of carbamazepine encephalopathy with neither excessive plasma level of the drug nor water intoxication. An idiosyncratic reaction is considered likely.