We describe a novel late-onset lysosomal lipid storage disease affecting a Tibetan terrier. The principal clinical manifestations include visual loss, progressive cerebellar ataxia and dementia. A necropsy of an affected 10-year-old dog demonstrated cerebellar atrophy. Histological analysis revealed extensive loss of retinal ganglion cells and cerebellar Purkinje cells, and mild to moderate loss of neurons in the cerebrum, basal ganglia and spinal cord. There were generalized neuronal hypertrophy and multifocal neuronal necrosis associated with the presence of enlarged macrophages. Neurons and perineuronal macrophages contained cytoplasmic granules that stained with PAS, luxol fast blue and several lectins. The granules were sudanophilic and autofluorescent. Electron microscopic analysis revealed lysosomes laden with lamellated membrane structures in neurons, pancreatic ductal and centroacinar cells and in cultured fibroblasts. These findings indicate lysosomal storage of both lipid and carbohydrate. Biochemical analysis of brain lipids and numerous lysosomal enzyme assays of leukocytes and cultured fibroblasts were unsuccessful in elucidating the underlying enzyme defect, although a generalized increase of brain gangliosides was noted.