Diabetic microangiopathy may be associated with the pathogenesis and progression of autonomic and peripheral neuropathy. In 17 long-standing type I diabetic patients with peripheral and autonomic cardiovascular neuropathy, several hemorheological and hemostatic alterations were found compared to 13 matched type I patients without neuropathy. In particular, increased plasma von Willebrand factor antigen (p less than 0.001), fibronectin (p less than 0.001) and fibrinogen (p less than 0.001) levels were demonstrated in neuropathic in comparison with non-neuropathic diabetic patients. Moreover negative correlations between these parameters and both motor and sensitive conduction velocity of median, sural and peroneal nerves were observed in diabetic patients with neuropathy. Higher blood viscosity (p less than 0.05 at shear-rate of 450 and 225 s-1; p less than 0.01 at 90 s-1; p less than 0.001 at 4.5 and 2.25 s-1), plasma viscosity (p less than 0.001) and lower erythrocyte filtrability (p less than 0.001) were also found in neuropathic compared to non-neuropathic diabetics. Increased prevalence of retinopathy (p less than 0.01) and nephropathy (p less than 0.001) was finally reported in patients with autonomic and peripheral neuropathy. Microvascular disease may be involved in the development of neuropathy in long-term type I diabetes mellitus.