Leukemia is a neoplastic disease with early oral and periodontal manifestations such as ulceration, infection, bleeding and gingival hyperplasia. This paper describes a 39-year-old pregnant woman with a diagnosis of acute myelomonocytic leukemia (AML), with gingival enlargement in the upper and lower jaws. A gingival biopsy was performed, followed by a complete blood count and peripheral blood smear. From a histopathological view, infiltration of the neoplastic (myelomonocytoblastic) cells was observed and many immature lymphoid cells were revealed by the hematologic tests. The interesting clinical finding about this case was the absence of spontaneous bleeding and profuse bleeding on probing. This case is reported to emphasize the leukemia-induced gingival enlargement in pregnancy and the early diagnosis of AML by dentists, which results in immediate treatment and management of the patient.