To assess the prognostic impact of cytogenetics in elderly patients with acute myeloid leukemia (AML) receiving intensive induction and consolidation treatment according to a single protocol specifically designed for patients above age 60, pretreatment samples from 361 patients registered for the AML HD98-B trial of the German-Austrian AML Study Group were analyzed by chromosome banding and fluorescence in situ hybridization, and cytogenetic findings were correlated with outcome. Using a proportional hazards model with backward selection, 3 prognostic subgroups were identified based on the influence of cytogenetic abnormalities on overall survival (OS): low-risk, t(15;17), and inv(16) in 25 of 361 patients (7%); standard-risk, normal karyotype, t(8;21), t(11q23), +8 within a noncomplex karyotype, and +11 within a noncomplex karyotype in 208 of 361 patients (58%); high-risk, all other aberrations in 128 of 361 patients (35%). On multivariate analysis, high-risk cytogenetics (hazard ratio [HR], 2.24) and age above 70 years (HR, 2.34) were independent prognostic factors affecting OS, and stratification according to these parameters demonstrated that a large subgroup of patients (55%), characterized by age 70 or older or high-risk cytogenetics, or both, had very unfavorable treatment results despite intensive chemotherapy. Thus, karyotype and age are major determinants of outcome in elderly patients with AML.