Pachygyria is a cortical malformation that results from the abnormal migration of neurons. Regions of the brain with pachygyria have an abnormally thick cortex that lacks normal folding and has deficient layering. We describe three siblings, born to nonconsanguineous Mexican parents, who have bilateral frontotemporal pachygyria without polymicrogyria. The pachygyria is accompanied by moderate mental retardation, esotropia, and either hypertelorism or telecanthus. They are otherwise morphologically normal and do not have microcephaly. Two experienced a single seizure in infancy. The characteristic phenotype present in this family suggests a new genetic syndrome that is likely inherited as an autosomal recessive trait. © 2003 Wiley-Liss, Inc.