The distinction between small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL) and mantle cell lymphoma (MCL) has important clinical implications. Typically, SLL/CLL is CD23+, whereas MCL is CD23-. However, CD23 is expressed in a subset of MCLs, and the clinicopathologic features of patients with these neoplasms are not well described. We report 18 CD23+ MCLs, detected by flow cytometry in all cases (dim intensity, 16; bright intensity, 2), 5 (28%), also positive by immunohistochemical analysis. There were 13 men and 5 women (median age, 56 years), 5 of whom died (median survival, 46 months). Seventeen (94%) had bone marrow involvement. Lymphadenopathy (14 cases [78%]), splenomegaly (11 cases [61%]), and leukemic involvement (10 cases [56%]) were common. Five cases (28%) had blastoid morphologic features. The frequency of CD23 expression by MCL is method-dependent, being typically dim and most commonly detected by flow cytometry. In this small study group, bone marrow and leukemic involvement were relatively common.