In patients with an impaired state of consciousness, EEG is fundamental, a correct neurological work-up. Cephalosporins have been identified as a case of triphasic waves' (TW) reversible encephalopathy. We report a case of an acute reversible encephalopathy with TWs during treatment with cefoperazone. We report the occurrence and regression of a confusional state with TWs encephalopathy at EEG after the administration of cefoperazone for urinary tract infection in a patient admitted for syncope. In conclusion, cefoperazone should be considered as a cause of toxic encephalopathy with EEG TWs, when there is a temporal relationship with its administration; EEG monitoring is useful in the neurological follow-up.