Cohen syndrome (MIM 216550) is an autosomal recessive disorder of unknown pathogenesis. The clinical manifestations of Cohen syndrome can be explained as a connective tissue disorder. We found a remarkably high level of urinary hyaluronic acid in 3 patients with Cohen syndrome. Hyperhyaluronic aciduria is a characteristic finding in Werner syndrome and some other conditions. We suggest that the basic defect of Cohen syndrome is associated with a metabolic abnormality in the extracellular matrix.