A male cat 12-14 weeks old had walking difficulties and an enlarged abdomen. Facial dysmorphism, plump paws, corneal clouding, granulation of neutrophils, vacuolated lymphocytes, and a positive urine test for sulfated glycosaminoglycans suggested mucopolysaccharidosis. Cultured fibroblasts incorporated 35SO4 into mucopolysaccharides more actively than did fibroblasts of a feline control, and degradation was far inferior. Activity of beta-glucuronidase was absent in leukocytes and markedly reduced in fibroblasts, thus establishing the diagnosis of mucopolysaccharidosis VII, a disorder previously described in humans, dogs, and mice. Light microscopic examination revealed foam cells in virtually all organs examined, and electron microscopic examination showed pancytic storage of floccular material characteristic of mucopolysaccharides. Stored sphingolipids in the form of zebra bodies were seen in ganglion cells of the central nervous system and in smooth muscle cells of blood vessels. This case represents another animal model of mucopolysaccharidosis VII with the full disease characteristics known in human patients.