Hematodermic CD4/CD56 neoplasm is a recently described entity. This name has been initially proposed by the French Study Group on Cutaneous Lymphomas which established the primary anatomoclinical and pathogenic and cytogenic bases of the disease in 1999. This descriptive and provisional name allowed conceptualizing the entity by its main clinical and phenotypical characteristics. The first case in the literature goes back to 1994. Since that time, several other cases have been published. The expression of CD56 led most of the authors to propose an NK-cell lineage origin. In the last WHO classification of lymphomas, the entity was indexed under the name of "blastic NK-cell lymphoma". However, the authors underlined that there were currently no clues to the etiology of blastic NK-cell lymphoma and that the precise lineage of this disease was still unresolved. At the clinical level the main characteristics of the disease are the skin tropism and the occurrence of a leukemic phase at any time during the course of the disease. The median age is 59 but pediatric cases do exist. At the morphological level skin biopsy shows a monomorphous cell proliferation simulating a pleomorphic T cell cutaneous lymphoma. The diagnosis is based on phenotypic criteria which require frozen tissue. Currently, the main characteristics are the expression of CD4 and CD56 antigens while the main defined lineage specific markers are negative (B-cell, T-cell, NK-cell and myeloid-cell lineages). The origin of the tumor cells still remains uncertain but the plasmacytoid dendritic cell is presently a very serious candidate. The tumor cells share a great phenotypical homology and particularly the expression of the CD123 antigen. Functional homologies have also been demonstrated with tumor cells in vitro. Outcome of CD4/CD56 hematodermic neoplasms is very bad. The median time of survival is 14 months irrespective of the treatment given. Conventional chemotherapies used for the treatment of aggressive lymphomas or acute myeloid leukemias are quickly inefficient.