CML is a rare disease in childhood and hematopoietic stem cell transplantation (SCT) remains the only proven option for cure of young patients (pts). We here report the results of the GPOH-trial “CML-paed”. From December 1995 to June 2004 pts younger than 19 years (median age: 11.4 yrs) with Philadelphia-chromosome positive CML (n=193; 99 boys, 94 girls) were treated by hydroxyurea ± interferon and scheduled for SCT from an HLA-matched family donor within 6 months after diagnosis (Dx) and from an unrelated donor within 12 months. 85% of the pts were diagnosed in chronic phase (CP). Six pts (3%) died from disease without SCT with a median interval from Dx to death of 6.5 months (range 0.5–12 months) and 25 pts are still searching for a donor. 168 pts underwent SCT (n=50 HLA-matched related; n=69 HLA-matched unrelated (MUD); n=18 HLA-mismatched related; n=31 HLA mismached unrelated) in CP (n=139), in accelerated phase (AP, n=9), in blast crisis (BC, n=9), or in 2. CP (n=10). Probability of overall survival (OS) was 75 % if SCT was performed <7 months after Dx (n=53 pts) and 60 % (n=100 pts) if pts were transplanted later, however, this difference was statistically not significant. Conditioning regimens included either total body irradiation (n=82) or busulfan (n=80) resulting in no statistically different impact on OS. 5-year OS was 82 % for SCT from HLA-matched related and 55% for HLA-MUD-SCT reflecting a higher transplant-related mortality for the latter (p=.0017). After SCT from HLA-mismached unrelated and HLA-mismatched related donors, OS was 56% and 50%, respectively. 12 out of 168 pts (12%) relapsed following SCT after a mean interval of 11 months (range: 1–137 mos) and 9 of them so far have died of CML. Outcome was inferior if SCT was performed in advanced stages of CML (OS of all pts in CP: 67%; in AP: 55%, in BC: 21%, respectively). During the last decade the 3-year OS after SCT from HLA-matched unrelated donors improved gradually from 45 % before the year 1994, to 53 % in the period 1995 to 1999 and to 62 % after 2000, respectively. This large series of pts from a controlled trial shows an excellent OS of 82% for pediatric pts with CML undergoing SCT from matched sibling donors and constantly improving results during the last decade in the setting of MUD-SCT.