This report presents the necropsy and biochemical findings on the first dog to die with alpha-L-iduronidase deficiency (mucopolysaccharidosis I, MPS I). Gross pathologic features, light- and electron-microscopic findings, and tissue enzyme, glycosaminoglycan (GAG), and sphingolipid levels are compared with the human disease counterpart and the previously described feline model. Results lend further support for the similarities of the canine disease and human MPS I.