Lymphoblastic leukemia is the most common malignant neoplasm of childhood, while lymphoblastic lymphoma comprises 2% of all non-Hodgkin lymphomas. Lymphoblastic leukemia/lymphoma derives from precursor B or T lymphocytes, and the term lymphoma is used for solid lesions with no or minimal peripheral blood and/or bone marrow involvement. Young children are the most commonly affected by B-lymphoblastic leukemia, whereas adolescents and young adults are the most commonly affected when the neoplasm manifests as a lymphoma, of either B- or T-cell phenotype. It is more common in males, and in its solid presentation, the lymph nodes and the skin are the most involved sites. In the oral cavity, extranodal lymphoblastic leukemia/lymphoma is more commonly derived from the immature B-cell lineage. The mandible and the surrounding mucosa are the most affected locations, presenting as painful swellings often associated with teeth displacement or mobility. Numb chin syndrome can also represent a manifestation of the disease. This neoplasm is characterized by a diffuse proliferation of small to medium-sized neoplastic cells, and the expression of TdT is typically observed. Pediatric patients have a more favorable prognosis, and survival rates depend on several prognostic factors; consequently, different therapeutic schemes are used to treat patients.