Three aged (10-year-old) German Shepherd Dog litter mates, separately reared, were affected with familial and adult onset peripheral neuropathy. They developed clinical signs, unsteady gait of their hind legs with progressive muscular weakness at almost the same time. The main lesions were systemic neurogenic muscular atrophy, segmental demyelination and Wallerian degeneration of the peripheral nerve fibres. Histochemically, collateral ramification and multiple terminal arborization were observed in terminal axons of motor neurones in the muscles. These changes were attributed to a dying-back process.