Although more than 12 years have passed since publication of the first WHO histological classification of central nervous system (CNS) tumours, the changes in this revised edition are not radical. Only one formerly recognized entity has been deleted: the monstrocellular sarcoma, because there is immuno- cytochemical evidence of its astrocytic nature. Several new tumour types have been added: the pleomorphic xanthoastro- cytoma has been generally acknowledged for almost a decade; the neurocytoma has gradually evolved as a clinical-pathological entity; and two new entries, the dysembryoplastic...