Two cases of an olfactory neuroblastoma are reported. The leading symptom was the increase in intracranial pressure. In spite of radical exstirpation—removal of the intracranial part including the infiltrated brain tissue as well as the part extending into the paranasal sinuses via a bifrontal transcranial approach—and postoperative radiation the tumour recurred in both cases. The survival time is now four and thirteen years. We suspect that neurologists and neurosurgeons have not always diagnosed the intracranial portions of these tumour correctly, because of their polymorphism. Wherever a tumour with the characteristics here described is encountered, we recommend that the diagnosis of olfactory neuroblastoma should be considered. Only in this way can the appropriate operative and postoperative therapy be correctly planned. The possible origins of the tumour are discussed in relation to the literature. Specific diagnostic features are mentioned and the therapy and prognosis are described.