Peripheral pancytopenia is a syndrome which allows for an early diagnosis, and although is may cover a large number of pathological entities, it can be clearly defined into three groups of illnesses which evolve with this syndromal manifestations. The first group includes non-neoplastic illnesses which include aplastic anemia, hemophagocytic syndrome associated to infection, immunological diseases and the deficiency of folates or vitamin B12. The second group includes neoplastic diseases as acute leukemia, non-Hodgkin lymphoma, and Hodgkin's lymphoma with myelofibrosis, malignant histiocytosis and non-hematological neoplasms, like the neuroblastoma and the embryonal rhabdomyosarcoma. The third group is formed by illnesses which have some similarity with neoplasms.