Hurler's syndrome is an inborn error of mucopolysaccharide metabolism leading to premature death in childhood. Allogeneic hematopoietic SCT can achieve long-term survival by correcting the enzymatic deficiency. In an attempt to improve long-term engraftment and to reduce regimen-related toxicity (RRT), a prospective multicenter approach was initiated in Germany using a fludarabine-based radiation-free preparative regimen. Between 2001 and 2008, 12 children were enrolled. Median age at SCT was 14 months (range, 4-31 months). The conditioning regimen contained fludarabine, BU, melphalan and antithymocyte globulin. CD34 positively selected PBSC were used in 10 children with a matched unrelated donor. Median cell dose was 24.6 x 10(6) CD34+ cells per kg (range 10.0-54.8). Two children with a matched sibling donor received non-manipulated BM. Donor lymphocyte infusions were given in 6/12 children for mixed hematopoietic chimerism. At a median follow-up of 29 months (range 2-85 months), all children engrafted and have either stabilized or improved neurological function. In total, 12/12 patients showed donor-derived engraftment with 9/12 having full and 3/12 having mixed hematopoiesis. One developed acute GVHD >or=grade II. RRT >or=grade II was observed in two patients.