A 40-year-old man presented to the hospital with acute onset of painful gingival swelling one week prior to admission. He noted occasional gingival bleeding when brushing his teeth, but reported that he otherwise felt well. He denied any fatigue, night sweats, weight loss, lymphadenopathy, abdominal pain, or other bleeding. He was not taking any medications.

Laboratory findings showed marked leukocytosis with a total white blood cell count 89.5 K/mm³ with 59.2% immature mononuclear cells on peripheral blood smear. He had a hemoglobin of 10.3 g/dL and platelet count of 127 K/mm³. Bone marrow biopsy demonstrated approximately 85% morphologic blasts/monoblasts with an abnormal myelomonocytic population identified on flow cytometry consistent with acute myeloid leukemia with monocytic differentiation.

Gingival overgrowth has many benign causes including pregnancy, long-standing gingivitis, and medications. It can also portend more serious systemic illness and hematologic disorders such as acute myeloid leukemia [1]. Oral manifestations may be one of the first clinical signs of leukemia, even without systemic symptoms [2], and gingival overgrowth should prompt a thorough history and exam for possible causes. If leukemia is suspected, a complete blood count should be obtained given the potential for serious complication if the diagnosis is missed.