The mucopolysaccharidoses, first described at the beginning of this century, are still subject of research. The accumulation of pathological metabolites and the underlying enzyme defects are now correlated to specific gene mutations. A comparison of genotype and phenotype of the individual forms of the mucopolysaccharidoses is the subject of ongoing studies. In many cases, symptomatic treatment was not able to increase the quality of life of patients suffering from mucopolysaccharidosis to a satisfactory degree. International working groups are, thus, currently trying to improve and standardize symptomatic therapies. A causal therapeutic approach was attempted by implanting different cells and tissues that are able to produce the missing enzymes. Bone-marrow transplantations were also performed, but both treatment approaches were not very effective and in some cases even proved fatal for the patients. An intensive international research effort focuses on enzyme-replacement therapy and gene therapy. Mucopolysaccharidoses are rare diseases, affecting only about one hundred patients in Austria. Nevertheless, Austria plays an active role in researching these metabolic disorders.