Objective: Chronic myelomonocytic leukemia (CMML) is a malignant hematopoietic disorder that shows clinical and pathological features of both myeloproliferative neoplasms (MPN) and myelodysplastic syndrome (MDS). It is manifested by monocytosis and cytopenias in peripheral blood, dysplasia in the bone marrow, structural symptoms and/or splenomegaly. It is the most aggressive of chronic leukemias and the risk of transformation to acute myeloid leukemia (AML) is significant (approximately 15% within 3-5 years after diagnosis) (1). According to the scoring systems, allogeneic hematopoietic cell transplantation (AHCT) would be the appropriate treatment method in fit patients, in the presence of high-risk disease and donor candidates, instead of hydroxyurea (HU) or hypomethylating agents (HMA) alone, used depending on the symptom. There are no standards such as an age limit, preparation regimen, stem cell source in the literature for stem cell transplantation in these patients. In this study, we summarized the treatments of our patients who underwent allogeneic stem cell transplantation due to CMML. Patients and Methods: Data from patients older than 18 years of age who underwent allogeneic transplantation due to CMML at our center between 2003 and 2019 were analyzed retrospectively. Patient files and the university’s electronic system were used for data collection. The data were processed with SPSS version 21.0. Results: The median age of 9 patients included in the study was 49 (34-64). 2 of the patients were women and 7 were men. 8 of the patients had CMML-2, 1 of them had CMML-1. The time from diagnosis to stem cell transplantation in CMML-1 patient was 95.8 months, and this patient was followed up for quite a long time without treatment. All patients received HU and HMA before transplantation. The median time from diagnosis to allogeneic transplant is 12.3 (3,-95.8) months. Bone marrow was used as a stem cell source in one of the patients, and peripheral blood was used in 8 patients. Myeloablative (BuCy, CyBu, TBF) regimens were used for 5 patients and reduced intensity (FluBu, CyTBI) preparation regimens were used for 4. The patients received a median of 5.2 (0.76-9.79) x 106/kg CD34 (+) stem cells. With allogeneic transplantation, 1 patient had transplant-related aplasic death, 1 patient had engraftment failure, 3 were refractory, and 4 patients had complete remission responses. In one patient, AHCT was performed with donor lymphocyte infusion (DLI). AHCT was applied twice in one patient. Recurrence was observed in one patient in the third month of the transplant. Since 4 of the patients died before the first 100 days, acute GvHD data could not be obtained. Other GvHH data are summarized in table 2. CMV was reactivated in 2 of the patients. As of the writing of this article, 8 patients have died and the causes of death are aplasia (1/9), infections and sepsis (3/9), primary graft failure (2/9), severe GvHD (1/9). 9), recurrent disease (1/9). Median overall survival is 18.3 (7-29) months. The 2-year overall survival probability is 33.3% (+/- 15.7), similar to the literature. Apart from these, 3 patients were engaged in AHCT after transforming to AML. Conclusion: In today’s conditions, if possible, clinical research options should be offered to every patient diagnosed with CMML first. If not possible, what will determine the course of treatment in high-risk CMML patients is their chance to tolerate intensive treatment options. AHCT is the only treatment with curative potential for high risk CMML. However, most of the high-risk CMML patients are patients with advanced age and comorbidities. Therefore, the majority of high-risk CMML patients can not undergo AHCT. In the literature, there is no randomized clinical study comparing allogeneic transplant with non-transplant treatments in CMML. The number of patients is small in most studies in the literature (2-4) and many studies, including ours, are retrospective studies. The prognosis of CMML is generally poor and survival has been reported between 20-40 months (5) (6). Similar results were obtained in our study (median 18.3 months). Overall survival was found significantly longer in patients who were taken to AHCN without transforming into acute leukemia in our series. The limitations of our study are the small number of patients, lack of the next generation sequencing of molecular markers and the retrospective nature of the study.