We determined prospectively the clinical and electrophysiological progression of idiopathic, diabetic, paraproteinemic, alcoholic, and B12 deficiency neuropathy in 606 subjects over 3 years. We hypothesized that idiopathic peripheral neuropathy would demonstrate slower progression when compared with other etiologies. Laboratory assessments were used to determine the etiology of peripheral neuropathy at baseline and after 3 years. When compared with peripheral neuropathy related to type 1 or type 2 diabetes mellitus, subjects with idiopathic peripheral neuropathy progressed much slower, but demonstrated similar rates of progression to that of the other groups. Overall, detectable progression was minimal over 3 years. After 3 years, only 3% of cases of idiopathic peripheral neuropathy had any potentially identifiable causes discovered. Clinical and electrophysiological detection of very slow progression for these five types of peripheral neuropathy is possible using currently established clinical scales and standard electrophysiological techniques.