Biphenotypic leukemias are rare in children and represent less than 5% of all histological subtypes of leukemias. Diagnosis requires careful assessment by cell morphology, genetics, and flow cytometry. The treatment goal is to eliminate the predominant clone, although there is no conclusive data about complete remission. Chemotherapy has shown better results than bone marrow transplant. Survival is influenced by therapy response and other factors inherent to the disease and the patient.Two patients diagnosed in 2009 are presented. The first patient was an 8 year-old girl who consulted for skin pallor, anemia, leukopenia, and presence of blasts in the white blood count. The second patient was a 10 year-old boy who complained of abdominal pain as result of peritonitis secondary to an acute appendicitis. The presence of blasts in peripheral blood was documented 48 hours after surgery. Cell morphology and flow cytometry confirmed the first case as acute lymphocytic leukemia, and the second as bilinear biphenotypic leukemia.