Major advances in the diagnosis, classification, and treatment of adult acute leukemias have resulted in significant increases in the number of complete remissions and long-term disease-free survivors. Despite these improvements, most adult patients with acute leukemias still eventually die from their disease or complications of its treatment. New experimental and clinical approaches used to diagnose, monitor, and treat these diseases hold promise for further increased cure rates in the future. This article reviews the classification, immunobiology, cytogenetics, diagnosis, and treatment of adult acute leukemias and describes new directions being taken toward their cure.