We report an 18-year-old boy who presented with seizures at the age of 12 years. He had 3 different kinds of seizures, occurring 4 to 5 times a week, despite adequate antiepileptic treatment. Magnetic resonance imaging (MRI) showed deep paramedian focal cortical dysplasia in the left parietal lobe. Ictal video-EEG demonstrated 5 seizures originating from the left parietal lobe, left hemisphere and right hemisphere. He was submitted to invasive recordings with two frontal strips and an interhemispherical grid that was advanced to the corpus callosum. The lesion and other seizure focuses were resected subpially down to the corpus callosum approximately I cm posterior to the motor area. His seizures resumed after three years of quiescence. Postoperative MRI investigation revealed remnants of dysplastic tissue deep in the interhemispheric region, which were silent during the invasive EEG monitorization. We want to re-emphasize that each patient with cortical dysplasia who is a candidate for epilepsy surgery should undergo detailed neuroradiological investigations as well as EEG monitorization, whereas complete resection of the lesion on the basis of findings that are obtained from neuroradiological examination might have a superior effect on the postoperative seizure Outcome compared to the findings obtained from EEG recordings.