A classification for childhood brain tumors based upon revision of nomenclature of all brain tumors published by the World Health Organization (WHO) in 1979 is proposed. Applicability of the WHO classification scheme was tested in a combined study of the clinical and pathologic features of approximately 3300 brain tumors in children. It was found to be adequate for many of the neoplasms but unsuitable for a significant proportion, including a number of complex cerebral tumors for which there was no appropriate name. Nomenclature of poorly differentiated or densely cellular neuroepithelial tumors was simplified to reflect the current state of knowledge of neuroembryology and neuro-oncology, although the Committee members recognized that such a proposal would likely perpetuate the long-standing and continuing controversy relative to the nature and origin of these neoplasms.