This protocol will examine whether the enzyme alpha-L-iduronidase (Laronidase), delivered into the spinal fluid of patients with Hurler syndrome at intervals before and after bone marrow transplant, is a safe and effective approach to slow the neurologic degeneration seen in Hurler patients undergoing transplantation.

Subjects will receive an infusion of Laronidase into his/her spinal fluid approximately 12 weeks before, 2 weeks before, 100 days after and 6 months after transplant. This procedure is done by lumbar puncture (also called a "spinal tap").

Inclusion Criteria:

• Patients with a diagnosis of MPS IH (Hurler syndrome) are candidates for this protocol if they are being considered for hematopoietic stem cell transplantation according the University of Minnesota guidelines.

Exclusion Criteria:

• Patients are less than 6 months old, or older than 3 years of age.
• There is a history of clinically-severe hypersensitivity to Laronidase.
• There is a contraindication for repeated lumbar puncture.
• The family is not willing to undergo the necessary procedures and evaluations inherent in the study.
• Consent has not been signed for participation in the 2004-09 study of intravenous Laronidase administration.