Leukemia is a malignant neoplasm of hematologic origin occurring from disorganized proliferation or increased life span of white cells. The initial manifestations of leukemia are generally signs of bone marrow failure, such as pallor, fatigue, fever, bleeding, and infection related to peripheral blood cytopenias. Few reports have described osteonecrosis, especially in the femoral head, as an initial manifestation of acute lymphoblastic leukemia. To the best of our knowledge, osteonecrosis of the jaw has not been reported as a first sign of leukemia. Here, two cases of osteonecrosis of the jaw as an initial manifestation of acute leukemia are reported, as well as a review of the literature regarding the main oral manifestations of leukemia. Keywords: acute lymphoblastic leukemia, first symptom, oral cavity