Polymicrogyria is a malformation of cortical organization. The aim of this historic cohort study was to describe clinical and EEG features of patients with polymicrogyria. Patients underwent clinical and neurologic examination and a prolonged routine EEG to allow recording during sleep. Neuroimaging data were classified as: perisylvian polymicrogyria (subdivided into holosylvian, posterior parietal, and generalized), hemispheric polymicrogyria, and frontal polymicrogyria. Forty patients were studied: 16 with holosylvian polymicrogyria, 14 with posterior parietal polymicrogyria, 4 with generalized polymicrogyria, 3 with hemispheric polymicrogyria, and 3 with frontal polymicrogyria. Patients with polymicrogyria usually did not have epilepsy and their EEGs were mostly normal (55%); the severity of the clinical and EEG features correlated with the extent of the cortical lesion. In perisylvian polymicrogyria, epileptiform abnormalities predominated in fronto-temporal regions. Dour patients had focal electrical status (FES) in awakeness and electrical status epilepticus of sleep (ESES); these four patients had right hemispheric polymicrogyria and asymmetric bilateral perisylvian polymicrogyria, mostly on the right hemisphere. The authors conclude that the EEG is usually normal in patients with polymicrogyria, despite it being associated with FES and ESES in certain patients.