The authors give a short report about the first-trimester prenatal detection of Hunter's disease (MPS II) inherited as X-linked disorder. There is written about a family having one affected child with Hunter's syndrome. Chorionic villus sample was taken at 10th weeks of gestation in the new pregnancy of the mother. The sex of the fetus was a male determined by DNA analysis. The activity of sulphoiduronate sulphatase was very low. The enzyme activity was also extremely low in the cultured cells from amniotic fluid taken at 16th weeks of gestation. On the basis of these results the pregnancy was terminated at parents's request. The diagnosis of Hunter's disease was confirmed by measuring the enzyme activity of the cultured fibroblasts from the male fetus.