Malformations of cortical development (MCDs) are increasingly recognized as important causes of developmental delay, epilepsy, and other neurological disorders. Polymicrogyria, a type of MCD, is characterized by many small microgyria separated by shallow sulci, a slightly thick cortex, neuronal heterotopia and often enlarged ventricles. The present descriptive study analysis the electroclinical and magnetoencephalographic findings of patients with epilepsy and polymicrogyria without schizencephaly. We studied six patients; mean age was 27 years, who had evidence of polymicrogyria in neuroimaging studies. A single equivalent-current dipole (ECD) model was used to estimate the location of epileptiform spike dipole sources. Analysis was performed on selected data segments containing MEG spikes. MEG results were combined with MRI to create magnetic source images (MSI). In all cases we present results of MRI, MEG, Video-EEG monitoring, and other functional neuroimaging studies if performed. MSI can be used to accurately localize sources of epileptiform discharges. As such MSI can play a role of directly determining the functional epileptogenic significance of abnormalities depicted in imaging. © 2004 Elsevier B.V. All rights reserved.