A 14-mo-old South American coati (Nasua nasua) was submitted for necropsy to the University of Kentucky Veterinary Diagnostic Laboratory. The coati had a history of progressive neurologic signs beginning 3 mo prior to euthanasia. At necropsy, the coati was in thin body condition, but no other significant findings were evident. Histopathologic findings included moderate distension of neuronal cell bodies by finely vesiculated cytoplasm within the cerebrum, cerebellum, spinal cord, and intestinal ganglia. Hepatocytes and macrophages in the lung, spleen, and liver were similarly affected. Transmission electron microscopy showed numerous electron-dense membranous cytoplasmic bodies, swirls, and vesicular profiles within neuronal lysosomes in the brain. To the authors' knowledge, this is the first report of a naturally occurring congenital glycogen storage disease in a South American coati and the family Procyonidae.