The leukemias can be divided into acute and chronic varieties, both of which have a myelocytic and lymphocytic type. When untreated, the acute leukemias are associated with a more rapid clinical course than are the chronic leukemias. Paradoxically, to the present time, the acute leukemias have been curable with chemotherapy, whereas the chronic leukemias have not. Until recently the treatment goal for patients with chronic leukemias has been to return the patient's life to normal for as long as possible. With recent advances, it may now be possible to cure some patients with chronic leukemia. Acute leukemias are treated with intensive chemotherapy, which is associated with severe and life-threatening side effects. Although this approach to treatment will cure some patients, the use of bone marrow transplantation has had an increasingly important role in the treatment of younger patients with these diseases.