Despite improvements in the achievement of complete remission and progress in the supportive care of adults with acute lymphoblastic leukemia (ALL) during the last decade, the majority of patients have eventually relapsed with overall survival in adult ALL of only 30~40%. However, recent therapeutic advances in allogeneic stem cell transplantation through the conduct of large collaborative studies, better understanding of the relevance of cytogenetics and molecular determinants, improved molecular techniques for the detection of minimal residual disease, and clinical research into novel biologic and targeted therapies have all combined to offer potentially a better hope for an improved outcome in this uncommon and difficult disease. Full knowledge of the molecular features associated with treatment response is required for precise leukemia prognostication and monitoring, and can provide clues to useful targets for novel therapies. (Korean J Med 78:36-48, 2010)