Circulating autoantibodies constitute a prominent feature of many autoimmune diseases. Recently, antibodies to interferon (IFN) have been recognized as an additional variant occurring spontaneously in about 10% of patients with autoimmune disorders. The reactivity of these antibodies appears to be restricted to IFN-alpha, with antibodies of individual patients recognizing unique epitope patterns. IFN antibodies are preferentially of the IgG type, and they likely constitute part of the normal B-cell repertoire. Whereas antibody titers differ largely among patients, the affinity of IFN binding has not been determined. Likewise, the mechanisms involved in IFN antibody synthesis as well as the clinical impact of these antibodies in autoimmune disorders remain elusive. Based on recent reports and our own observations, this article reviews current knowledge regarding occurrence and properties of IFN antibodies associated with autoimmune conditions. From clinical and experimental evidence, mechanisms possibly involved in IFN antibody production are derived and the significance of antibody-mediated sequelae is evaluated.