For chronic idiopathic axonal polyneuropathy (CIAP), even after extensive evaluation, no cause has yet been found. Considering the age and sex distribution of patients with this disease, it is possible that vascular disease plays a role in the development of this polyneuropathy. As endoneurial vessel abnormalities can be related to ischemia, we investigated endoneurial vessels in sural nerve biopsies of 18 patients with CIAP. As controls we used sural nerves of 4 patients with diabetes mellitus, 6 patients with hereditary motor and sensory neuropathy type II (HMSN type III) and 10 autopsy cases. Basal lamina area thickness, endothelial cell area, lumen area, and the number of basal laminae, endothelial cells and periendothelial cell nuclei were investigated. Basal lamina area thickness, endoneurial cell area and number of endothelial cell nuclei in CIAP were increased in comparison with HMSN type III, whereas the basal lamina area thickness of patients with CIAP and diabetes mellitus were in the same range. The structure of the basal lamina area in CIAP differed from diabetes mellitus; in diabetes mellitus there was a larger number of lamellae, whereas in CIAP there was an increase in collagen. There was no correlation between basal lamina area thickness and age. In CIAP patients with peripheral vascular disease of the legs, basal lamina area thickness was increased. The relation between basal lamina area thickening and peripheral vascular disease of the legs in CIAP may indicate a role for ischemia in the development of this polyneuropathy.