Monocytosis is a common hematologic abnormality, and most often secondary to an underlying condition. In the absence of any identifiable cause, a clonal origin should be considered, prompting investigation for a hematologic malignancy. Chronic myelomonocytic leukemia is a complex disease, overlapping features of both myelodysplastic and myeloproliferative syndromes. It is characterized by monocytosis associated with cytopenias, myeloid proliferation, and the presence of splenomegaly. In more aggressive forms, there is a risk of leukemic transformation, and allogeneic stem cell transplantation remains the only curative option.