Acute myeloid leukemia with t(8;21)(q22;q22) is a distinct type of leukemia considered to have a favorable prognosis. However, some patients rapidly succumb to disease despite chemotherapy. We studied 56 patients with acute myeloid leukemia associated with t(8;21) and correlated clinicopathologic, cytogenetic and molecular findings with outcome to identify markers of prognosis. In a subset of patients, we also assessed the status of the c-KIT, FLT3 and RAS genes. There were 31 men and 25 women, with a median age of 38 years (range 4-76). The follow-up period ranged from 17 to 104 months (median 52). At the last follow-up, 29 patients had died, 25 patients were in complete remission and two patients were alive with disease. The median survial was 38 months. The 5-year overall survival rate of newly diagnosed patients was 56%. Most patients (39/56, 70%) had chromosomal aberrations in addition to t(8;21), with loss of a sex chromosome (39%) being most common followed by del(9q)(q21-22) (11%) and trisomy 8 (7%). These aberrations, however, did not predict survival. C-KIT (D816V or D816Y), FLT3 (ITD or D835) and RAS mutations were detected in 26, 10 and 7%, respectively, of cases assessed. The 5-year overall survival rate of patients with mutated leukemia was 20%. No mutations were observed in three patients who died within 7 months of diagnosis. Leukocytosis or CD56 expression did not correlate with a poor survival nor did the levels of CD19 expression predict c-KIT mutation status. We conclude that acute myeloid leukemia associated with t(8;21) is a heterogeneous disease with poor survival in a subset of patients unrelated to common secondary cytogenetic aberrations.