Sanfilippo Syndrome or Mucopolysaccharidosis Ill (MPS Ill) is a group of lysosomal storage diseases resulting from a deficiency of one of four lysosomal enzymes: Type A - heparan N-sulfatase (SGSH), Type B - a-N-acetylglucosaminidase (NAGLU), Type C - acetyl CoA a-glucosaminide acetyltransferase (HGSNAT) and Type D - N-acetylglucosamine-6-sulfatase (GNS). Each of these enzymes is necessary for degradation of heparan sulfate. Deficiency of any of these enzymes manifests as a neurodegenerative disorder with accompanying somatic manifestations. Typically this presents early in life with developmental delays followed by developmental regression and usually results in death sometime during the second decade of life, though several less severe cases have been described living into late adulthood (30's to 60's). Often there is a delay of several years from time of symptom onset to diagnosis. Currently treatment is limited to supportive care. We will briefly discuss the typical natural history and presumed pathophysiology of the disease. We will also discuss current experimental therapies being pursued for treatment of this devastating disease. These include enzyme replacement, gene therapy, stem cell therapy, and substrate reduction approaches.