We report 5 cases of Aggressive Natural Killer-Cell Leukemia (ANKL) diagnosed and treated in our institution within a period of 5 years. Presented are the clinical, hematological, immunophenotypic, immunogenotypic and cytogenetic data. ANKL is a very rare disorder. On review of the English-language literature only 68 published cases were identified. Analysis was performed on a total number of 73 cases (68 from the literature and the series of 5 presented hereby). Presented and discussed are the epidemiology, clinical picture, morphology, cell marker, immunogenotype, cytogenetics, and survival data of the analysis, as well as the associations with the Epstein-Barr virus (EBV). To our knowledge this is the largest series of cases of ANKL analyzed and therefore it is hoped to contribute towards a better characterization of the disorder.