Acute lymphoblastic leukemia/lymphomas are tumors made of the precursor B or T cells. Precursor B cell type presents as acute leukemia, and most cases of pediatric leukemia are of this type. Malignancies originated from T cells are less common and are often manifested as lymphoma in adolescents. Terminal deoxynucleotidyl tranferase (TdT) is a DNA polymerase that is present in immature pre-B and pre-T cells. TdT enzyme is a sign of cell immaturity and is used to differentiate the dominant types of lymphoblastic lymphoma from mature lymphoma/leukemia cells. TdT is expressed in 90%–95% of lymphoblastic lymphoma cells. Childhood TdT negative lymphoblastic leukemia/lymphoma is very infrequent and its prognostic significance remains challenging. It is suggested that TdT negative lymphoblastic leukemia/lymphoma shows poor response to chemotherapy and has a more disastrous course. Here, we report a case of TdT negative T-cell lymphoblastic lymphoma in a 10-year-old boy who presented with respiratory distress.