A COMMON pediatric complaint is the failure of an infant to thrive. Among such infants there will occur an occasional patient who will demonstrate a characteristic symptom complex known as the diencephalic syndrome. This symptom complex, as described by various authors,1-8 is typical enough to set these patients apart from other marasmic infants (Table). The diencephalic syndrome results from neoplasms in the area of the hypothalamus and the third ventricle and has its onset during the first halfyear of life with a fatal termination before 2 years of age. Definite emaciation without depression of the sensorium is the rule, and the classical patient will have the triad of marasmus, euphoria, and nystagmoid eye movements. The purpose of this paper is to present a case of the diencephalic syndrome along with a review of the literature and previously reported cases. Report of a Case This was the first admission of