The pathology of the peripheral nerves in a dog with naturally occurring giant axonal neuropathy (GAN) is described. Axonal swellings were found predominantly in the distal portions of the tibial and recurrent laryngeal nerves. Excess neurofilaments, often arranged in whorls, were present in the swellings which were found in both myelinated and non-myelinated fibres. Other axonal organelles tended to be isolated in small pockets and on occasions adaxonal Schwann cell processes partially separated these organelles from the axoplasm. The myelin sheath was attenuated over the swellings and short lengths of demyelinated axon were often seen adjacent to the enlargements. Some Schwann cells also contained excessive microfilaments. The peripheral nerve pathology in the dog appear closely similar to that of human GAN and to certain experimental toxic neuropathies, particularly those produced by n-hexane and methyl-butyl ketone.