Cerebellar medulloblastoma has been recognized as a distinct clinicopathological entity; however, its origin and its differentiating capacity are still disputed because of the primitive nature of the tumor cells. To assess the nature of so‐called medulloblastoma, 12 cases of medulloblastoma‐neuroblastomas, two primitive neuroectodermal tumors (Rorke's NOS category) and two cerebral neuroblastomas were studied. Moreover, some mature neuronal tumors, and some glial and mesenchymal tumors as controls, were examined by electron microscopy and immunohistochem‐istry using a panel of the antibodies. The relatively high frequencies of neuronal differentiation in the so‐called medulloblastoma and the paucity of glial differentiation, albeit with the absence of similar neurofilament immuno‐reactivity in the neoplastic cells, suggest the histogenesis of these neoplasms is more closely aligned with the histogenesis of neuronal elements in the central nervous system.Human β4 tubulin isotype (TuJl) first becomes positive when primitive neuronal neoplastic cells start to form neuritic processes from the cytoplasm. A maturation‐associated switch from vimentin filament synthesis to (34 tubulin may occur in the primitive neuronal neoplastic cells. TuJl is a reliable marker of neu