In the congenital bilateral perisylvian syndrome, pseudobulbar symptoms, cognitive deficits and cortical malformations in the perisylvian region are typical features. We report two initially magnetic resonance imaging (MRI) negative patients from our epilepsy surgery program that shared the same seizure and ictal SPECT characteristics suggesting seizure onset localized in the perisylvian region. In one patient, reevaluation revealed perisylvian cortical malformation on MRI while in the other patient MRI was normal. In these patients, subtraction ictal SPECT coregistered with MRI (SISCOM) proved useful together with clinical data in diagnosing the patients with mild forms of perisylvian syndrome.