The recent World Health Organization (WHO) classification recognizes three subtypes of marginal zone lymphoma (MZL): extranodal MZL of mucosa-associated lymphoid tissue (MALT), splenic MZL and nodal MZL. As a group, MZL share morphological and immunophenotypic features similar to that of the marginal zone B-cell in secondary B-follicles, the postulated common cell of origin. There is, however, increasing information about molecular heterogeneity between the types of MZL, suggesting different aetiology and highlighting our current incomplete understanding of this evolving entity. We describe the presentation and clinical course of three patients with MZL who do not fit the currently recognized WHO categories, and best fit the putative category of MZL, leukaemic subtype. We review the current literature on this newly described entity, highlighting the importance of its recognition.