All the diseases in question here are rare. The most common, mucopolysaccharidosis (MPSosis III), occurs at a rate of 1 in 160000. Consequently, any one doctor will only encounter a few cases as a rule, and the literature offers mainly casuistic descriptions. Up till now, there has been no systematic and comprehensive review. We thus felt that it would be of interest and benefit to prepare a collective report on a large body of material gathered over a period of many years, the material being extensive enough to provide adequate possibilities for making comparisons. In so doing, we were also able to describe for the first time the specific, and, in some cases, the pathognomonic symptoms for each disease.