IN RECENT years increasing attention has been paid to the biochemical handicap in mucopolysaccharide metabolism shown by the children with Hurler's disease or with other forms of the Hurler-Hunter syndrome. Many reports have described the clinical features of individual typical patients, usually when advanced in manifestation, as an illustration of the bodily handicaps which accompany the demonstrated abnormality in the tissue and urinary mucopolysaccharide levels. No articles, however, have been directed toward early diagnostic problems and eventual natural history of an inclusive series of children in each of the phenotypic categories. The biochemical classification of the various subdivisions of the Hurler-Hunter syndrome is still imperfect, and prognostication and genetic counselling must rest at present on accurate classification of the pediatric patient on clinical grounds. Some major patterns with consistent expression and significant incidence have emerged, though certain patients show the abnormal mucopolysaccharide excretion but have clinical manifestations beyond the current