We report a 19-year-old man who presented to our facility with medically intractable, symptomatic generalized epilepsy manifesting as generalized tonic-clonic seizures (GTCs). Before he underwent an anterior callosotomy (6 cm), these seizures, which he had experienced for 11 years, seemed to have a left-sided focal origin. Intraoperatively, no epileptiform discharges were found on the electrocorticogram (ECoG) performed prior to sectioning, but more than 10 left-sided seizures were recorded after sectioning. In the 10 years since surgery, the patient's seizures have remained generalized; however, the frequency and severity of the seizures have decreased. These findings indicate that the presence of electrocorticographic seizures, as measured by ECoG immediately following callosotomy, may not predict a poor surgical outcome, even though such a finding might be indicative of epileptogenicity in general.