Following reports of childhood acute myeloid leukemia (AML) showing that patients with t(9;11)(p22;q23) have a better prognosis than those with translocations between 11q23 and other chromosomes, we compared response to therapy and survival of 24 adult de novo AML patients with t(9; 11) with those of 23 patients with other 11q23 translocations [t(11q23)]. Apart from a higher proportion of French-American-British (FAB) M5 subtype in the t(9;11) group (83% v 43%, P = .006), the patients with t(9;11) did not differ significantly from patients with t(11q23) in terms of their presenting clinical or hematologic features. Patients with t(9;11) more frequently had an extra chromosome(s) 8 or 8q as secondary abnormalities (46% v 9%, P = .008). All patients received standard cytarabine and daunorubicin induction therapy, and most of them also received cytarabine-based intensification treatment. Two patients, both with t(9;11), underwent bone marrow transplantation (BMT) in first complete remission (CR). Nineteen patients (79%) with t(9;11) and 13 (57%) with t(11q23) achieved a CR (P = .13). The clinical outcome of patients with t(9;11) was significantly better: the median CR duration was 10.7 versus 8.9 months (P = .02), median event-free survival was 6.2 versus 2.2 months (P = .009), and median survival was 13.2 versus 7.7 months (P = .009). All patients with t(11q23) have died, whereas seven (29%) patients with t(9;11) remain alive in first CR. Seven of eight patients with t(9;11) who received postremission regimens with cytarabine at a dose of 100 (four patients) or 400 mg/m2 (2 patients) or who did not receive postremission therapy (2 patients) have relapsed. In contrast, 7 (64%) of 11 patients who received intensive postremission chemotherapy with high-dose cytarabine (at a dose 3 g/m2) (5 patients), or underwent BMT (2 patients) remain in continuous CR. We conclude that the outcome of adults with de novo AML and t(9;11) is more favorable than that of adults with other 11q23 translocations; this is especially true for t(9;11) patients who receive intensive postremission therapy.