The differential diagnosis based on morphology between neuroblastoma (NB) and peripheral neuroepithelioma (PN) is difficult, since these tumors share many architectural and cytological features. In this study, a morphometrical approach to this diagnosis is made by using nuclear (shape factors) and tissue (volume density of nuclei and stroma) parameters. Quantitative morphological analysis adds important information, which when used with clinical and biochemical data facilitates the distinction. In the majority of cases, nuclei of PN are significantly less round than those of NB and their profile is much more irregular. The density of neoplastic nuclei is significantly higher in PN. However, in a certain number of cases, even the morphometrical study confirms how difficult it may be to differentiate these two neoplastic entities, since the values of parameters are largely overlapping. This suggests the existence of a "continuum" of changing features between NB and PN, which may substantiate the hypothesis of a common histogenesis.