A global, observational disease registry has been established to characterize the course of disease and track clinical outcomes in patients with Mucopolysaccharidosis Type I (MPS I), a rare and treatable lysosomal storage disorder. This report outlines procedures for data collection and presents the recommended minimum schedule of assessments that comprise the disease-specific clinical and laboratory parameters that are tracked in the database. Aggregate data are summarized for the first 302 patients enrolled, representing entries from 24 countries. The median current age of the patients is 9.0 years (range: 0.4-64.8). Syndrome diagnoses include 47% Hurler (severe form), 25% Hurler-Scheie (attenuated form with an intermediate phenotype), 13% Scheie (most attenuated form), and 15% unknown. Younger ages at symptom onset and disease diagnosis are associated with the severe Hurler syndrome, but there is overlap among syndromes. Diagnosis was delayed by years to decades in several patients with Hurler-Scheie and Scheie syndromes. Patients with symptom onset before age 5 are more likely to have a gibbus, cognitive impairment, and pneumonia, whereas patients with symptom onset above age 5 are more likely to have carpal tunnel syndrome, myelopathy, and glaucoma. Cardiac valve abnormalities, joint contractures, corneal clouding, and hernia are reported by over 70% of patients regardless of the age of symptom onset. Approximately 80% of the patients have received enzyme replacement therapy, hematopoietic stem cell transplantation, or both. Overall, the MPS I Registry database contains a broad sample of the global patient population, providing a potentially useful tool for expanding knowledge of MPS I and facilitating evidence-based decisions about the optimal means of monitoring and treating affected individuals.