Familial macrocephaly with mesodermal hamartomas is described as a distinct syndrome in nine individuals from four families. Constant manifestations include symmetrical macrocephaly without ventricular enlargement, mild neurological dysfunction, and postnatal growth deceleration. Speech and motor delays observed in all the children were usually well compensated by adulthood. Two children had mild mental retardation and seizures which may have been related to intracerebral hemorrhage in one. Mesodermal hamartomas were present in affected persons from all four families, with 60% of individuals manifesting only discrete lipomas and hemangiomas. More serious tumors, including intracerebral hemangiomas, hemangiomatous involvement of the bone, and aggressive lipomas occurred in 40%. Other findings that make it possible to delineate a recognizable syndrome include down-slanting palpebral fissures (66%), a high palate (67%), joint hyperextensibility (55%), pectus excavatum (22%), strabismus or amblyopia (33%), and prolonged drooling (44%). The Bannayan-Zonana syndrome is an autosomal-dominant trait with male predominance of affected individuals.