Mucopolysaccharidosis VI (MPS VI) results in accumulation of the glycosaminoglycan (GAG) dermatan sulfate. Storage of GAG may be relieved by Naglazyme® treatment. The Clinical Surveillance Program (CSP) is a voluntary observational program which collects data to characterize progression of MPS VI and collect long term efficacy and safety outcomes of Naglazyme treatment based on patient standard of care assessments. Of the 151 patients enrolled in the CSP through 22 March 2011, 12 entered enrollment in the prior year and 139 have received Naglazyme treatment. To date, 6 patients have had bone marrow transplant (BMT), 2 of which were reported to not remain grafted, and 5 of the 6 patients have received subsequent Naglazyme treatment. There was an approximately 50% decrease in median urinary GAGs from baseline after Naglazyme treatment for up to 9 years. Improved endurance measurements (12-minute walk and 3-minute stair climb tests) and increased height and weight from baseline were observed in Naglazyme treated patients. Elevated antibody levels were not correlated with changes in urinary GAGs. Occurrences of serious adverse events related to Naglazyme treatment, including infusion related events, remain low. Naglazyme treatment appears to slow progression of MPS VI when compared to untreated patients in the CSP Conflict of Interest declared.