Chronic inflammatory demyelinating polyneuropathy (CIDP) is an autoimmune disease that targets the myelin sheaths of peripheral nerves. In clinical practice the diagnosis is often difficult to make because of the clinical heterogeneity of the disease, its multifocality and predilection for proximal nerve segments, and the limitations of our electrophysiologic and pathologic techniques. Although there are rather stringent research criteria for selecting patients to clinical trials, there are no generally agreed-on clinical diagnostic criteria for CIDP, and application of the research criteria to routine clinical practice would miss the diagnosis in a majority of patients. Because of this uncertainty, the prevalence of CIDP is greatly underestimated, and patients are often left untreated despite progression of their disease. However, given what is known about the clinical presentation and pathophysiology of CIDP, patients with neuropathy of otherwise unknown etiology are more likely to have CIDP than idiopathic axonal neuropathy, and warrant a trial of therapy if they have nerve conduction velocities below the lower limits of normal, prolongation of F-waves beyond the normal range, or presence of conduction block or temporal dispersion. A favorable response to therapy, consisting of stabilization or improvement of the neuropathy, would confirm the diagnosis.