We explored the long-term follow-up of continuous spike-and-wave complexes during sleep (CSWS) in polymicrogyria and the anatomic volumetric variables that influence the risk of developing this age-related epileptic encephalopathy.We performed prospective follow-up of 27 patients with polymicrogyria/CSWS (mean follow-up 14.3 years; range 2-31 years) and comparative volumetric analysis of the polymicrogyric hemispheres and ipsilateral thalami vs 3 subgroups featuring polymicrogyria without CSWS, benign rolandic epilepsy (BRE), and headache. Receiver operator characteristic analysis of the power of volumetric values was determined to predict CSWS.CSWS peaked between 5 and 7 years (mean age at onset 4.7 years). Remission occurred within 2 years from onset in 21%, within 4 years in 50%, and by age 13 years in 100%. We found smaller thalamic and hemispheric volumes in polymicrogyria/CSWS with respect to polymicrogyria without CSWS (p = 0.0021 for hemispheres; p = 0.0003 for thalami), BRE, and controls with headache (p < 0.0001). Volumes of the malformed hemispheres and ipsilateral thalami reliably identified the risk of incurring CSWS, with a 68-fold increased risk for values lower than optimal diagnostic cutoffs (436,150 mm(3) for malformed hemispheres or 4,616 mm(3) for ipsilateral thalami; sensitivity 92.54%; specificity 84.62%). The risk increased by 2% for every 1,000 mm(3) reduction of the polymicrogyric hemispheres and by 15% for every 100 mm(3) reduction of ipsilateral thalami.The polymicrogyria/CSWS syndrome is likely caused by a cortico-thalamic malformation complex and is characterized by remission of epilepsy within early adolescence. Early assessment of hemispheric and thalamic volumes in children with polymicrogyria and epilepsy can reliably predict CSWS.