Diphenylhydantoin is a anticonvulsivant and antiarrhythmic drug. We reported a less frequent case of diphenylhydantoin associated acute hepatotoxicity in a 18-year old woman who immediately after child birth presented generalized tonic-clonic seizures secondary to arachnoid cyst in the left temporal-lobe. The patient developed a mononucleosis like coinciding with previous descriptions. Histological features observed in the liver biopsy specimen showed compatible changes with toxic acute liver failure (ALF). In the few cases published of ALF for Diphenylhydantoin is not specifically pointed out the absence of hepatic encephalopathy as it happened to our patient.