Advances in neuroimaging techniques have enabled the recognition of developmental malformations of the brain during life. Careful correlation of clinical and imaging features has identified several new syndromes. We have studied 31 patients with a congenital neurological syndrome characterised by pseudobulbar palsy, cognitive deficits, and bilateral perisylvian abnormalities on imaging studies. All patients had diplegia of the facial pharyngeal, and masticatory muscles, of variable severity. Some patients had slight dysarthria, whereas others were unable to speak. 85% of patients had mental retardation, ranging from mild to severe. Epilepsy was present in 27 (87%) and commonly consisted of atypical absence, atonic/tonic, tonic-clonic seizures, and, less frequently, partial attacks. Seizures were poorly controlled in 55%. Magnetic resonance imaging showed bilateral perisylvian cortical malformations consistent with polymicrogyria, confirmed at necropsy. Division of the corpus callosum in several patients resulted in seizure improvement. This congenital bilateral perisylvian syndrome can be clinically diagnosed and confirmed by imaging studies. Further studies are necessary to elucidate its cause.