Characteristically, mantle cell lymphoma (MCL) expresses surface immunoglobulin (sIg), CD19, CD20, and CD5 and lacks CD10 and CD23. Rare CD5-MCL variants have been described. This report describes a case of leukemic MCL with morphologically and immunophenotypically distinct classic MCL and blastoid-variant MCL (BV-MCL) components. The classic MCL had typical morphologic features and immunophenotype (kappa sIg light chain-restricted and CD5+; CD10- and CD23-). The BV-MCL had larger nuclei and open chromatin; these cells also were kappa sIg light chain-restricted; however, they were CD10+ and CD5-. Fluorescence in situ hybridization studies demonstrated cyclin D1-immunoglobulin heavy chain gene fusion in both components; the bone marrow biopsy cellularity was replaced by CD10+ and cyclin D1+ and CD5-BV-MCL. This case illustrates the phenotypic heterogeneity of MCL and underscores the need for histopathologic correlation and, in some instances, ancillary genetic studies to accurately classify B-cell lymphomas.