Mucinous ovarian tumors are still a subject of controversy because they can show either intestinal or endocervical differentiation. Morphologic distinction between borderline and malignant tumors is sometimes difficult, and their clinical behavior has not been definitively ascertained. We selected 10 mucinous cystadenomas (MCAs), 32 intestinal mucinous borderline tumors (IMBTs), and 15 well-differentiated mucinous carcinomas (MCCs), all with goblet cells, at least focally. In all cases, we studied the Clinicopathologic features, mucin content, intermediate filament expression, and some nuclear quantitative features, namely, the volume-corrected mitotic index (M/Vi), percentage of nucleolated nuclei, mean number of nucleoli per nucleus, percentage of nucleoli touching the nuclear membrane, and mean nuclear area. The quantitative nuclear study included cytometric DNA analysis and the results were expressed as relative mean ploidy value (RMPV) and as diploid-tetraploid or aneuploid histograms. The results of the quantitative study were evaluated statistically. All patients had stage IA tumors, had received surgical therapy only, and were alive and well after a follow-up of more than 5 years. Light microscopic examination revealed that destructive stromal invasion was not present in any MCCs and that IMBTs and MCCs were easily recognizable using the Hart and Norris criteria, later expanded by Hart. Mucin histochemistry and intermediate filament immunohistochemistry failed to detect substantial differences between the diagnostic categories. DNA analysis demonstrated an increase in aneuploid tumors going from IMBTs to MCCs, but these differences were not statistically significant. On the other hand, nuclear quantitative morphology showed significant differences among the three groups of tumors for all features considered. Forward stepwise discriminant analysis highlighted that MCAs, IMBTs, and MCCs were contiguous but different categories. These data support the separation of IMBTs and MCCs into morphologically different categories as underlined by the results of quantitative nuclear morphologic analysis. The favorable outcome of all patients confirms the excellent prognosis of stage I IMBTs and suggests that well-differentiated MCCs without destructive stromal invasion at stage IA could be assimilated, in terms of prognosis and therapy, into stage I IMBTs.