There is no standard treatment for adolescents aged 15 years or older with acute lymphoblastic leukemia (ALL), although this age group has been reported as having a poorer prognosis compared to younger patients. We retrospectively analyzed the outcomes of three consecutive Tokyo Children's Cancer Study Group ALL trials (1995-2006) of 373 patients aged 10 years or older, with particular focus on adolescents aged 15-18 years (older-adolescents n = 41), compared to those aged 10-14 years (younger-adolescents n = 332). The probability of event-free survival at 8 years was 67.5 ± 7.4 % for the older-adolescents and 66.5 ± 2.6 % for the younger-adolescents (p = 0.95). Overall survival was 70.7 ± 7.1 % for the older-adolescents and 74.3 ± 2.4 % for the younger-adolescents (p = 0.48). The differences between groups in relapse incidence, non-relapse mortality, and death rate during induction were not statistically significant, although the older-adolescents trended towards a higher frequency of having stem-cell transplantation during the first remission. In conclusion, our treatment strategy, which consists of intensive induction and block-type consolidation, provided improved outcomes for patients aged 15-18 years, comparable to those for patients aged 10-14 years.