One hundred ninety-six patients with acute myelogenous leukemia (AML) were treated with intensive induction chemotherapy using similar daunorubicin/cytarabine/thioguanine regimens. Treatment results of 44 patients who had a documented preleukemic syndrome or cytopenia present for more than 2 months before developing over AML were compared with 152 patients with de novo AML. Eighteen (41%) patients with preleukemia evolving into AML achieved complete remission compared with 111 (73%) patients with de novo AML (P less than .01). Patients with preleukemia-AML had a significantly longer period to recovery of granulocytes. Multivariate analysis indicated that presence of a previous preleukemic syndrome and advancing age were independent poor prognostic indicators for achieving remission. For patients who achieved remission, disease-free survival and overall survival were also inferior for patients with previous preleukemia; disease-free survival was 17 +/- 17% at 3 years compared with 29 +/- 10% in patients with de novo AML (P = .02). These data indicate that intensive chemotherapy has limited efficacy in patients with AML following a preleukemic syndrome. Durable remissions may be achieved in some patients.