The authors report three patients with neurofibromatosis type 1 and different types of malformations of cortical development: Patient 1 had a possible transmantle cortical dysplasia involving the right temporoinsuloparieto-occipital areas; Patient 2 had a periventricular band of heterotopic gray matter with an overlying pachygyric cerebral cortex; and Patient 3 had a left perisylvian polymicrogyria. Because all of these lesions result from different pathogenetic mechanisms, neurofibromin may play a role during several stages of cortical development.