A 9-mo-old neutered male Labrador Retriever developed severe hypoglycemia, collapse, and seizures after consuming a large quantity of sugar-free gum sweetened with the sugar-alcohol xylitol. The dog was treated with i.v. boluses and continuous infusion of dextrose; its condition improved rapidly, but the dog remained mildly hypoglycemic for 11 hours before recovering fully. In humans, xylitol has little to no effect on plasma insulin or glucose levels, but in dogs xylitol is a strong promoter of insulin release and can cause severe hypoglycemia with ataxia, collapse and seizures. With the increased appearance of xylitol-sweetened products in the US, xylitol toxicosis in dogs may become more common.