In the WHO classification, there is a provisional entity called Myelodysplastic/Myeloproliferative Neoplasm, Unclassifiable (MDS/MPN, U). Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T) was included in this category. Recently published studies report a small percentage of patients with RARS-T. Sixty percent of these have JAK2 V617F mutation, which can suggest the coexistence of two pathological conditions (MDS and MPN). In this paper, we analyzed three patients diagnosed with RARS-T in the Department of Hematology, "Fundeni" Clinical Institute, Bucharest, Romania, during the period 2005-2011. The patients were investigated with cytogenetic exam and molecular biology. In these three cases were identified morphological features of multilineage dysplasia (two-lineage dysplasia in two cases and three-lineage dysplasia in one case). In two cases, thrombocytosis was under 1000×10(3)/μL and clinical evolution was similar to the myelodysplastic syndrome (transfusion dependent anemia with response to administration of erythropoietin). In the third case, the platelets were over 1000×10(3)/μL and with response to the treatment with Hydrea, which improved anemia. JAK2 V617F mutation was not identified in any case. RARS-T remains a provisional entity and requires a complex investigation of patients for the correct diagnosis of these patients. Therapeutic options should be personalized to each case in part because there is not yet a standardized treatment of these patients.