Acute lymphoblastic leukemia affects infants, children, adolescents, and adults. Although most children have a high likelihood of cure, outcomes in adults have much room for improvement. In between lies the adolescent and young adult population, not only in terms of age but also in clinical success rates. This review describes biology, prognostic factors, and treatment approaches in adolescents and young adults with acute lymphoblastic leukemia. Assessing the outcomes in adult and pediatric clinical trials that enroll adolescents and young adults can be especially useful in determining how best to treat these patients. Current new treatment strategies are also discussed.