We reviewed eight cases that were diagnosed before 1995 with B-prolymphocytic leukaemia (B-PLL) harbouring t(11;14)(q13;q32) and/or cyclin D1 staining. Thirteen B-PLL patients without t(11;14) were selected as controls. Peripheral blood, bone marrow and histological sections were re-examined without cytogenetic information. Final diagnosis was made using morphology, cytogenetics, immunophenotype and immunohistochemistry. Clinical characteristics were similar for both groups except for younger age, male predominance and extranodal involvement in cases with t(11;14). CD5 was more frequently positive in the t(11;14)+ group (80%) than in the t(11;14)- group (31%). Surface membrane immunoglobulin was strongly expressed by all t(11;14)+ cases, but only 45% of t(11;14)- cases. Histopathological and cytological review of cases with t(11;14) showed an infiltrate with a mixture of cells, some resembling prolymphocytes and others with mantle cell lymphoma (MCL) morphology. Blood films of cases with t(11;14) showed features suggestive of B-PLL in three, and in others, a mixture of cells resembling MCL and nucleolated ones; none corresponded to the blastoid form of MCL. We suggest that 'B-PLL' with t(11;14) may represent a splenomegalic form of MCL evolving with leukaemia. These cases illustrate the importance of tissue diagnosis with cyclin D1 staining and fluorescence in situ hybridization analysis in B-cell leukaemia with prolymphocytic features.