Although neuropathy has long been recognized as a complication of diabetes, the impact of this condition has not been adequately established. The prevalence of diabetic neuropathy is virtually unknown because the published studies differ considerably with regard to definition, method of assessment, and patient selection. Furthermore, the determination of prevalence has been hampered by the fact that there is no generally accepted classification of the variety of manifestations of diabetic neuropathy. The introduction of new sensitive diagnostic methods aids in the detection of less severe stages of neuropathy, as compared with clinically based assessment, and renders the disease more prevalent. The prevalence of diabetic neuropathy in the few reported population-based studies was approximately 30%. We have evaluated the prevalence of cardiovascular autonomic neuropathy in a group of approximately 1000 diabetic patients randomly included from 21 hospitals in Germany, Austria, and Switzerland. The results of this study and those of a prospective study on the natural history of neural dysfunction during the first 5 years after diagnosis of type 1 diabetes will be presented.