The prognostic impact of trisomy 8, alone or with other clonal aberrations, was evaluated in 849 patients with previously untreated acute myeloid leukemia (AML) who were registered to 5 Southwest Oncology Group trials. At presentation, 108 (12.7%) patients had ؉8 in their karyotypes, including 43 (5.1%) patients with ؉8 as the sole aberration; 307 (36.2%) were normal, and 434 (51.1%) had other cytogenetic abnormalities. Patients with ؉8 were slightly older (P ؍ .033), had lower WBC (P ؍ .011), and had lower percentages of peripheral blasts (P ؍ .0004) than the patients without ؉8. Median survival time for all patients with ؉8 was 9.9 months (95% CI, 6.5-12.5), similar to that of "unfavorable" cytogenetics risk groups (8.3 months; 95% CI, 6.8-9.5.) Patients with ؉8 had significantly lower peripheral blasts (P ؍ .0002), WBC (P < .0001) counts, and decreased overall survival (OS) than patients with normal cytogenetics (9.9 months vs 15.4 months; P ؍ .006).However, survival of patients with ؉8 as the sole aberration did not differ significantly from those with normal cytogenetics (P ؍ .36). Thus, the trisomy 8 group as a whole had poor survival, which was largely attributable to worsened outcomes among patients whose trisomy 8 was associated with other unfavorable cytogenetic abnormalities. (Blood. 2002; 100:29-35)