Monoclonal gammopathy is responsible for about 10% of acquired peripheral neuropathies of unknown origin. Monoclonal gammopathy is the result of uncontrolled proliferation of a single clone of plasma cells producing the first class of immunoglobulin (M-protein). The routine diagnostic process of peripheral neuropathy requires electrophysiological studies and several laboratory tests, including the immunoelectrophoresis or immunofixation of serum proteins. Monoclonal gammopathies develop in malignancy, immunological disorders, chronic infections and as so-called "benign form" or monoclonal gammopathy of undetermined significance (MGUS). Lymphoproliferative malignancy may develop in MGUS after many years of disease. Patients with MGUS-associated neuropathy should be carefully evaluated, and if malignancy is not found the progress of the disease should be monitored. We present four patients with peripheral neuropathy associated with monoclonal gammopathy. These cases represent different forms of this type of neuropathy and well illustrate the necessity of looking for monoclonal gammopathies in peripheral neuropathy.