We studied three cases of primitive neuroectodermal tumors surgically removed from the cauda equina region of adults. There was no clinical or radiological evidence of cerebellar medulloblastoma, other intracranial tumor or paraspinal sympathetic neuroblastoma. Two patients died: autopsies revealed no primary intracranial neoplasm. One patient is alive 3 years after surgery with no detectable intracranial tumor. The tumors had the light and electron microscopic features of primitive neuroectodermal tumors as described earlier in the literature. In addition, in all three cases many tumor cells could be stained for cytoplasmic neurofilament antigen.