Ultrastructural and morphometric studies were performed longitudinally to characterize the topographic distribution of autonomic neuropathy in the BB-rat. Four levels of predominantly sympathetic nerves were examined. Typical axonal dystrophic changes were consistently increased in diabetic rats and were found to be most severe in the prevertebral celiac ganglion, the mesenteric nerve, the superior cervical ganglion, and the paravertebral ganglion, in that order. Dystrophic changes were also demonstrated in postsynaptic dendrites. In addition, the diabetic mesenteric nerve displayed progressive nerve fiber atrophy and fiber loss. We conclude that dystrophic and degenerative axonopathy is a reproducible structural hallmark of diabetic sympathetic neuropathy. It does not appear to be an accentuation of an age-related phenomenon, but rather, it is caused by the persistent diabetic dysmetabolism.