This chapter showcases a patient suffering from Lennox-Gastaut syndrome due to perisylvian polymicrogyria. The 10-year-old right-handed boy had a history of dysarthria and seizures. He started having seizures at 3 years of age. He was diagnosed with Lennox-Gastaut syndrome and underwent several unsuccessful trials of valproate, clobazam, phenobarbital, clonazepam, phenytoin, carbamazepine, and lamotrigine. Excellent control was finally achieved with topiramate 200 mg/day; for the past 4 years, he has averaged one generalized tonic-clonic seizure a year. On examination, he presented with striking dysarthria, drooling, moderate restriction of tongue movements, difficulty in whistling and blowing, and abnormally brisk jaws jerk. Deep tendon reflexes were hyperactive. Brain magnetic resonance imaging (MRI) revealed bilateral perisylvian polymicrogyria. The main features of perisylvian syndrome are pseudobulbar palsy, cognitive deficits, and epilepsy. The variability of the clinical picture is remarkable. Not all patients present with all the main features. On the contrary, they may present with soft signs, as was the case in this patient's mother. She had no complaints and had never been examined. Dysarthric speech seems to be the main feature of this syndrome, and it occurs in approximately 75% of patients. Variable cognitive deficits and epilepsy occur in 50-75% of patients. Lennox-Gastaut syndrome may be medically treated and sometimes responds well to treatment with antiepileptic drugs. It is an age-dependent epilepsy syndrome with many different possible etiologies. © 2008 Elsevier Inc. All rights reserved. 316318Guerreiro, M.M., Andermann, E., Guerrini, R., Familial perisylvian polymicrogyria: a new familial syndrome of cortical maldevelopment (2000) Ann Neurol, 48, pp. 39-48Kuzniecky, R., Andermann, F., Guerrini, R., Congenital bilateral perisylvian syndrome: study of 31 patients (1993) Lancet, 341, pp. 608-612Palmini, A., Gambardella, A., Andermann, F., Intrinsic epileptogenicity of human dysplastic cortex as suggested by corticography and surgical results (1995) Ann Neurol, 37, pp. 476-487