A young adult female Siamese cat born of a mother-son mating was referred because of dwarfism, facial abnormalities, severe skeletal deformities, multifocal neurologic deficits, and retinal atrophy. Cats of similar appearance had been observed in a previous litter of the same parents. Metachromatic inclusion bodies were demonstrated in circulating leukocytes. The urine contained a high concentration of mucopolysaccharide, as detected by the toluidine blue spot test. The uronic acid content of the cetylpyridinium chloride-precipitable mucopolysaccharide in the urine was 17 times greater than that in the urine from a control cat of the same age and breed.