Hematopoietic stem cell transplantation (SCT) is the only proven cure for chronic myeloid leukemia (CML), a rare disease in childhood. We report outcomes of 314 children with Philadelphia-chromosome-positive (Ph+) CML undergoing SCT from HLA-matched siblings (n = 182) or volunteer-unrelated donors (VUD; n = 132). Three-year overall survival (OS) and leukemia-free survival (LFS) rates were 66% and 55% (n = 314). For 156 children in first chronic phase (CP1) who underwent transplantation from HLA-identical siblings, OS and LFS rates were 75% and 63%. For 97 children who underwent SCT in CP1 from VUD, 3-year OS and LFS rates were 65% and 56%, reflecting higher transplantation-related mortality (TRM) after VUD SCT (35% vs 20%; multivariate hazard ratio [HR], 1.9; 95% confidence interval [CI], 1.0-3.5; P =.05). In a multivariate model for OS and LFS, outcomes were superior in CP1 than in advanced phase (AP/CP1) (OS HR, 2.0; 95% CI, 1.3-3; P =.001; LFS HR, 1.8; 95% CI, 1.2-2.6; P =.003). For relapse, donor source (VUD/sibling) (HR, 0.38; 95% CI, 0.19-0.76; P =.006) and disease stage (AP/CP1) (HR, 2.4; 95% CI, 1.36-4.3; P =.003) were significant. This is the first large series to show that SCT confers long-term LFS in most children with CML and helps assess alternative therapy, including tyrosine kinase inhibitors.