With an histological, immunohistochemical study of 7 cases of olfactory esthesioneuromas (4 of them had an ultrastructural study), our purpose was to revise the problem of the too often ambiguous terminology and of the different histological lower classes classifications of these tumors. Our own results and the literature demonstrate that they are polymorphic. In standard histology, they are often right diagnosed but an immunohistochemical study can be useful and an ultrastructural study absolutely necessary for a reliable diagnosis. For an easier nomenclature, we advise to use only one terminology for these tumors = olfactory esthesioneuroma. But, because of their important polymorphism, we keep to an histological lower classes classification according to their degree of differentiation in light microscopy: well differentiated tumors (old esthesioneuroepitheliomas), moderately differentiated tumors (old esthesioneurocytomas), poorly differentiated tumors (old esthesioneuroblastomas and so on described as neuro-endocrine carcinomas by Silva and al).