Age at diagnosis remains one of the strongest prognostic factors in acute lymphoblastic leukemia (ALL), with older patients having inferior outcomes compared with younger patients. Adolescents and young adults (AYAs) with ALL (age 15-30 years) represent a patient subgroup with distinctive biology whose optimal therapy has yet to be determined. Compared with younger children with ALL, AYAs are more likely to present with unfavorable presenting characteristics (such as high presenting leukocyte counts, T-cell phenotype, and the Philadelphia chromosome). Additionally, AYAs with ALL experience more regimen-related toxicity than younger patients. Recent retrospective studies suggest that patients age 15 to 21 years treated on pediatric ALL regimens have better outcomes than similarly aged patients treated on adult ALL regimens. Pilot prospective studies are under way to test the feasibility of administering pediatric ALL regimens to AYAs with ALL, with promising preliminary results.