Thirty patients with intractable partial epilepsy and a pathological or radiological diagnosis of neuronal migration disorders (NMD) were studied at the Montreal Neurological Institute and Hospital, Montreal, Quebec, Canada. Age at onset of epilepsy ranged from 4 months to 21 years (mean 5.7). Prenatal etiological factors in 8 patients included maternal x-ray exposure or trauma, diabetes, advanced maternal age, uterine abnormality. All patients had partial epilepsy: complex partial (67%), partial motor (73%), and secondary generalized seizures (73%). 8 patients (27%) had tonic or atonic drop attacks, and 6 of these had lesions involving the central region. Status epilepticus had occurred in 30%. A below average IQ was found in 1/2 of the patients. MRI was superior to CT, but did not distinguish between pachygyria, cortical dysplasia or tuberous sclerosis. White matter subcortical abnormalities were demonstrated more frequently than cortical abnormalities. In 22 of 26 surgically treated patients, the histological diagnosis was focal cortical dysplasia (12), and forme fruste of tuberous sclerosis (10). Those with a histological picture of tuberous sclerosis had none of the classical clinical diagnostic signs, but 80% had delayed psychomotor development and all 10 patients had multilobar unilateral or bilateral EEG spiking. These findings differed from patients with focal cortical dysplasia whose developmental milestones were normal and epileptogenic discharges were confined to one lobe or area of the brain. [1]