The acute leukaemias are a group of neoplastic diseases that are characterized by proliferation of immature white cells in the bone marrow and/or blood and are often associated with severe leukopenia, anaemia and thrombocytopenia. Oral manifestations are more common in patients with acute leukaemia. Oral bleeding, gingival enlargement, ulceration and infection in patients with leukaemia have been described. Leukaemic infiltrates in the gingivae are commonly seen in acute monocytic leukaemia. A case of acute monocytic leukaemia in a 34-year-old female who reported with gingival enlargement is presented here. The role of oral lesions as a diagnostic indicator is discussed.