"Refractory anemia with ring sideroblasts and thrombocytosis" (RARS-T) is a rare disease, a provisional entity, with a controversial status in the 2008 revised WHO classification. Even at present time, RARS-T is a matter of debate whether it is a distinct clinicopathological entity or more likely a constellation of clinical and pathological features of two well-defined myeloid neoplasms, myelodysplastic syndrome and myeloproliferative neoplasm. Perhaps none of the clonal disorders illustrates better the challenges presented by the current classification of myeloid neoplasms, than this clinical entity with overlapping features of both refractory anemia with ring sideroblasts and essential thrombocythemia. The purpose of this study is to present the evolution of such a case, with difficulties in establishing not only the correct diagnosis, but also the appropriate therapeutic approach. For this reported case, we present documented details regarding persistent thrombocytosis, slightly increased number of leukocytes and analysis of Janus kinase 2 (JAK2) genes that revealed a V617F mutation, confirming the presence of an underlying myeloproliferative neoplasm, followed later in the evolution by occurrence of myelodysplastic features as ring sideroblasts. This case might interest pathologists, but especially clinicians, for at least two reasons: the rarity of this disease and the lack of data on prognosis of these patients, probably because of relatively recent established diagnosis criteria and existence of few studies with small number of patients. The third interesting aspect for practitioners would be the absence of consensus on optimal clinical treatment for this disorder, because there are few cases that meet the rigorous diagnostic criteria.