The mucopolysaccharidoses and mucolipidoses are recessively inherited lysosomal storage diseases. Each of the disorders can now be specifically identified in cultured fibroblasts. As a group these disorders clinically present with a Hurler-like phenotype. Genetic heterogeneity and variable expression of the same enzyme deficiency require a combined clinical and laboratory approach to the diagnosis of these disorders. This feature is demonstrated by mucopolysaccharidosis I. This diagnosis refers to a specific deficiency of the lysosomal enzyme alpha-L-iduronidase. Further characterization requires clinical assessment to determine whether the final diagnosis is the Hurler syndrome, the Scheie syndrome or the Hurler-Scheie compound. Clinically each of these three disorders may be difficult to distinguish from other mucopolysaccharidoses or mucolipidoses. There is no specific treatment currently available for any of these disorders. However, a specific diagnosis should be established in each case to insure an accurate prognosis (some of these disorders are compatible with near normal life expectancy and normal intelligence), appropriate genetic counseling for the family and timely use of prenatal diagnosis by amniocentesis which is available for each of these disorders.