Myelodysplastic syndromes (MDS) are a heterogeneous group of hematological malignancies characterized by dysplasias, ineffective hematopoiesis and risk of acute myeloid leukemia transformation. Approximately 90% of MDS patients present mutations in genes involved in various cell signaling pathways. Specialized DNA polymerases, such as POLN, POLI, POLK, POLQ, POLH, POLL and REV3L, insert a nucleotide opposite replication–blocking DNA lesions in an error-prone manner and, in this way, sometimes can actively promote the generation of mutation. For the best of our knowledge, has not been described the mutations of these genes in MDS. DNA target sequencing CDS regions of the REV3L gene was performed in a 58-year-old man diagnosed as High Risk Myelodysplastic Syndrome. The patient presented very low hemoglobin, increased number of blasts, karyotype:47,XY,+8[6]/47,XY,del(7)(q32),+8[7], no response to hypomethylating therapy (decitabine), all markers of poor prognosis. Target sequencing identified a mutation c.9253-6T>C REV3L (Substitution - intronic) with VAF (variant allele frequency) = 16% considered pathogenic according to Functional Analysis through. Hidden Markov Models (FATHMM). This is the first evidence of REV3L mutation in MDS and, of utmost importance, associated with poor prognosis.