The lysosomal storage disorder (LSD) mucopolysaccharidosis type I (MPS I, McKusick 25280, Hurler syndrome, Hurler-Scheie syndrome, Scheie syndrome) is caused by a deficiency in the lysosomal enzyme, alpha-L-iduronidase (EC 3.2.1.76). MPS I patients can present within a diverse clinical spectrum, ranging from classical Hurler syndrome to attenuated Scheie syndrome. Laronidase (Aldurazyme) enzyme replacement therapy has been developed as a treatment strategy for MPS I patients and has been approved for clinical practice. Here we review the pre-clinical studies and clinical trials that have been used to demonstrate that intravenous laronidase therapy is well tolerated and effective for treating MPS I patients who do not have neuronal pathology. Current challenges for a viable treatment strategy for all MPS I patients include development of an early screening protocol that identifies patients before the onset of irreversible pathology, methods to predict disease severity, appropriate treatment for neuropathology, and an effective patient monitoring regimen.