OBJECTIVES: Hurler syndrome is characterized by progressive multisystem deterioration leading to early death in childhood. This prospective study evaluated the long-term outcomes of patients with Hurler syndrome who underwent umbilical cord blood transplantation from unrelated donors. STUDY DESIGN: Only patients with Hurler syndrome who underwent umbilical cord blood transplantation between December 1995 and March 2006 (n = 25) and who were followed for at least 5 years (n = 19) were included in the analysis. The patients were longitudinally evaluated by a multidisciplinary team of specialists following a standardized protocol. RESULTS: Median age at transplantation was 15.9 months (range 2.1-35), and patients were followed up until a median age of 10.1 years (range 7.2-14.9). Overall survival was 80%. All successfully transplanted patients achieved full donor chimerism and normal enzyme levels, and all children continue to make gains in development. Gross motor function was the most affected area. Vision and hearing were compromised in a minority of the patients, with some requiring corneal transplant or hearing aids. Cardiopulmonary function improved. Some children required orthopedic surgery, but severe complications were prevented in most patients. Although longitudinal growth was lower than that of unaffected children, it was considerably higher than expected from the natural course of the disease. Head circumference normalized. Hydrocephalus was not observed at longer follow-up, and cerebral atrophy decreased over time. CONCLUSIONS: In this descriptive study of children with Hurler syndrome, unrelated umbilical cord blood transplantation was associated with improved somatic disease and neurodevelopment.