We report one new case of congenital hypothalamic hamartoblastoma syndrome (Pallister-Hall syndrome) and one case of a diencephalic nodule associated with craniofacial malformations. Based on a review of 11 cases of Pallister-Hall syndrome documented by pathological examination, two cases presumed by phenotype, three cases of hypothalamic hamartoma with craniofacial anomalies only, and several cases of related interest, we delineate the clinical, neuroradiologic, and neuropathologic manifestations which aid in differential diagnosis. Clinical manifestations in infants with Pallister-Hall syndrome included postaxial polydactyly with nail dysplasia, short nose with flat nasal bridge, apparently low-set, posteriorly angulated ears, kidney and lung anomalies, congenital heart defects, imperforate anus, and micropenis with undescended or hypoplastic testes in males. These manifestations were associated with varying degrees of panhypopituitarism and pituitary aplasia. In three cases of hypothalamic hamartoma associated with craniofacial anomalies only, the face resembled that of holoprosencephaly. Other cases of hypothalamic hamartoma have had associated palate or heart defects or presented with precocious puberty. Of the infants with a hypothalamic hamartoblastoma at autopsy, neuropathologic findings were consistent with a primitive neuroectodermal tumor. Surgical tissue from our sole survivor suggested such tumors might mature, and the tumor has not recurred. Neuroradiologic diagnosis may be difficult but should be attempted in infants with these clinical manifestations; due to the need for prompt initiation of appropriate therapy.