Studies are reported of 10 children having physical findings previously reported in cases classified as showing cerebral gigantism. These findings included mental retardation; advanced height, weight, and bone age; and a characteristic facies. Six had pneumoencephalography and all showed communicating hydrocephalus. Karyograms were normal. Urinary 17-KS steroid excretion was increased for chronologic age, but levels were compatible with physiologic age. Adrenal response to dexamethasone suppression and metyrapone administration was normal. The condition is regarded as a reflection of congenital central nervous system dysfunction with mental retardation and altered hypothalamic control of anterior pituitary function.