Atypical Chronic Myeloid Leukemia, BCR-ABL1 negative (aCML) is a rare hematological entity, included in the group of myelodysplastic (MDS)/myeloproliferative (MPN) overlap syndromes. It is characterized by an aggressive course, a high rate of acute myeloid leukemia (AML) transformation, and a dismal outcome. The clinical presentation includes splenomegaly and leukocytosis with neutrophilia and left-shifted granulocytosis accompanied by granulocytic dysplasia and sometimes multilineage dysplasia. In past years, the disease incidence was likely underestimated, as diagnosis was only based on morphological features. Recently, the improving knowledge in the molecular biology of MDS/MPN neoplasms has made it possible to distinguish aCML from other overlapping syndromes, basing on next generation sequencing. Among the most commonly mutated genes, several involve the Jak-STAT, MAPK, and ROCK signaling pathways, which could be actionable with targeted therapies that are already used in clinical practice, opening the way to tailored treatment in aCML. However, currently, there are few data available for small samples, and allogeneic transplant remains the only curative option for eligible patients.