The prognosis for adult acute lymphoblastic leukemia (ALL) remains poor, which contrasts with that for pediatric ALL. It is regarded that the prognostic diversity is attributable to several differences between adults and children with respect to biological characteristics of leukemic cells, tolerance to anticancer drugs, treatment itself, and so on. It has been reported that adolescent ALL patients who were treated according to the pediatric protocol had a significantly better survival than those who were treated according to the adult protocol, indicating that the difference of treatment may be of considerable importance. To test the hypothesis, the Japan Adult Leukemia Study Group (JALSG) has planned a phase 2 study to treat younger ALL patients who are negative for BCR-ABL with the pediatric regimen which was used by the Japan Association of Childhood Leukemia Study. Those who are positive for BCR-ABL can participate in a separate protocol. The regimen is especially characterized by dose-intensified L-asparaginase, high-dose methotrexate, and intensified maintenance therapy.