beta-glucuronidase deficiency in fibroblasts, leucocytes and in serum and increased urinary excretion of mucopolysaccharides were found in a girl, now 13 years old, who exhibits some features of a mucopolysaccharidosis such as moderate mental deficiency, craniofacial dysmorphism, a short neck, protruding sternum, vertebral deformities and corneal clouding. Coarse granulations were found in her leucocytes. The liver and spleen are not enlarged and there is no gingival hyperplasia. Additional features, hitherto undescribed, are hydronephrosis and defective ossification of the medial carpal and tarsal bones. Low enzyme activity in the parents and a normal brother suggests heterozygosity.