Children with myeloid leukemia associated with Down syndrome (ML-DS) have superior outcome compared with non-DS patients, but suffer from higher constitutional cytotoxic drug susceptibility. We analyzed the outcome of 170 pediatric patients with ML-DS enrolled in the prospective, multicenter, open-label, nonrandomized ML-DS 2006 trial by Nordic Society for Pediatric Hematology and Oncology (NOPHO), Dutch Childhood Oncology Group (DCOG), and Acute Myeloid Leukemia-Berlin-Frankfurt-Münster (AML-BFM) study group. Compared with the historical control arm (reduced-intensity protocol for ML-DS patients from the AML-BFM 98 trial), treatment intensity was reduced by lowering the cumulative dose of etoposide (950 to 450 mg/m) and intrathecal central nervous system prophylaxis while omitting maintenance therapy. Still, 5-year overall survival (89% ± 3% vs 90% ± 4%; = .64), event-free survival (EFS; 87% ± 3% vs 89% ± 4%; = .71), and cumulative incidence of relapse/nonresponse (CIR/NR; 6% ± 3% vs 6% ± 2%; = .03) did not significantly differ between the ML-DS 2006 trial and the historical control arm. Poor early treatment response (5-year EFS, 58% ± 16% vs 88% ± 3%; = .0008) and gain of chromosome 8 (CIR/NR, 16% ± 7% vs 3% ± 2%, = .02; 5-year EFS, 73% ± 8% vs 91% ± 4%, = .018) were identified as independent prognostic factors predicting a worse EFS. Five of 7 relapsed patients (71%) with cytogenetic data had trisomy 8. Our study reveals prognostic markers for children with ML-DS and illustrates that reducing therapy did not impair excellent outcome. The trial was registered at EudraCT as #2007-006219-2.