Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder that is characterized by the presence of an absolute monocytosis (1 × 10^ 9/l) in the peripheral blood, the overlap of myelodisplastic aspects and myeloproliferative aspects in the bone marrow and tendency to transform into acute myeloid leukemia. CMML is considered to be the most aggressive chronic myeloid leukemia. We present the case of a 48 years old woman who was hospitalized in March 2013 in the Center of Hematology and Bone Marrow Transplantation for anemia related symptoms. Initial investigations showed anemia, relative monocytosis (10% monocytes of the WBC differential) with an increasing absolute number of monocytes (> 1,000/μl) in the following months. Initial exploration of the bone marrow (aspirate and bone marrow biopsy and immunohistochemistry IHC tests) revealed elements of trilinear dysplasia and an increased percentage of myeloblasts (11-14%). In the next four months myeloblasts percentage remained below 20% (8-14%) and it has been observed a gradually increasing of monocytoid elements (> 20%). Immunophenotyping in the bone marrow aspirate identified a monocytic proliferation with high percentage (8%) of immature cells. The karyotype reported the presence of clones with t (1;3). Initially diagnosed as RAEB-2 (WHO) the case was recomitted in CMML-type 2 with a progression to acute myeloid leukemia (AML). Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been performed after getting the best possible therapeutic response with AML chemotherapy type (complete remission). Allo-HSCT was performed using myeloablative conditioning, 12 months after diagnosis. The patient is now in complete remission, 24 months after allo-HSCT.