Leukemic infiltration of the gingiva is most commonly reported to be associated with monocytic subtypes of acute myeloblastic leukemia (AML) but rarely with myelodysplastic syndromes (MDS). Here we report a case of CD56+ chronic myelomonocytic leukemia (CMML) who developed gingival involvement simultaneously when the leukocyte count elevated. At that time no increase in peripheral or bone marrow blasts were observed. Gingival hypertrophy regressed with the treatment of hydroxyurea. Three months later, bone marrow blast count elevated and the patient was treated with two courses of AML-like regimen and then one course of consolidation therapy. The patient is in complete hematological remission for one and a half years. Similar to other extramedullary involvements, gingival hypertrophy in CMML can be a harbinger of the disease entering a more aggressive phase requiring systemic chemotherapy.