BACKGROUND Co-occurrence of other autoimmune disorders (AID) and autoantibodies in patients with autoimmune demyelinating CNS disorders have not been studied previously in patients of Indian origin. OBJECTIVE To determine the frequency of concomitant autoimmune disorders, anti-nuclear antibody (ANA) and antithyroid antibody (ATAb) and to evaluate the impact on clinical course of disease. METHODS A total of 111 patients with MS and 152 patients with non-MS demyelinating disorders were included. Demographics, clinical course and disability were recorded. History of other autoimmune disorders (AIDs) in patients and first degree relatives was noted. Serum ANA and ATAb were tested. RESULTS Concomitant AIDs were seen in 21% of MS and 19% of non-MS patients. Autoimmune thyroid disease was most frequent and seen in 10.8% of MS and 6.6% of non-MS disorders. Frequency of ATAb was significantly higher among MS group (MS 25.5% vs non-MS 13.2% P = 0.04) but that of ANA was similar between the 2 groups (MS 19.8% vs non-MS 26.9% P = 0.17). A positive family history of autoimmune disorders was noted in 20% of MS and 15.1% of non-MS disorders. Clinical course was unaffected by presence of concomitant AID and autoantibodies. CONCLUSIONS Cooccurrence of autoantibodies and AID are seen in a significant number of patients with MS and non-MS disorders and influences clinical management.