Only 1 to 2% of all non-Hodgkin's lymphomas (NHL) present with an enlarged spleen, most of them "small B-cell lymphomas." Recently, several reports have identified these lymphomas as marginal zone B-cell lymphomas. We reviewed 39 cases of NHL presenting with an enlarged spleen without lymphadenopathy, documented by fixed and frozen material. Two were peripheral T-cell lymphomas, four diffuse large B-cell lymphomas, and 14 hairy cell leukemias. The remaining 19 belonged to the "small B-cell" category and constitute the focus of our study. Subtyping was achieved by combining morphology, immunophenotype, and cytogenetic features according to the proposal of the International Lymphoma Study Group; in addition, analysis of the peripheral blood and bone marrow smears was performed adopting the French-American-British (FAB) criteria. From this study, we can conclude that most "small B-cell" NHL of the spleen were either mantle cell lymphomas or marginal zone cell lymphomas and, by peripheral blood analysis, that the mantle cell lymphomas corresponded to intermediate lymphocytic lymphoma and the marginal zone cell lymphomas to splenic lymphomas with villous lymphocytes. As a result, several diagnostic criteria can be proposed that may be helpful in differentiating mantle cell lymphoma from marginal zone cell lymphoma in the spleen.