Mucopolisaccharidoses (MPS) are a group of disorders resulting from the accumulation of glycosaminoglycans in the cell (Table I). Under normal conditions, these macromolecules are digested by hydrolytic enzymes in the lysosomes. When the enzymes are absent or their activity is impaired, glycosaminoglycans accumulate leading to enlargement of the cell and tissue damage with organ dysfunction. Enzyme replacement therapy (ERT) is a relatively effective method for treatment of MPS patients, who up till now, could be treated by palliative care only (Table II). Currently, ERT is available to patients with MPS type I, II and VI. In each type of the disease, the absent enzyme is replaced by repeated intravenous infusions. ERT has been proven successful in minimising the major symptoms in patients and, consequently, improving their quality of life. The enzyme does not cross the blood-brain barrier, thus it has no influence upon neurological abnormalities.