['Infectious agents have been suspected as a triggering factor for development of autoimmune thyroid disease (ATD). Some reports from Western countries have suggested association between Helicobacter pylori (HP) infection and ATD.', 'To investigate the association of ATD with Cag A seropositivity in a population with high rate and early age of onset of HP infection.', 'IgG anti HP and anti Cag A antibodies were measured in 88 patients with ATD and compared with results of 112 healthy individuals.', "The rate of infection with HP was not significantly different in patient and control groups, but there was significant association between ATD and infection with Cag A strains (p<0.005). This association was significant for both hypothyroidism (p<0.005) and Graves' disease (p<0.02). Cag A antibody level correlated with titers of thyroid auto antibodies (p<0.001)."] Is infection by Cag A positive strains of Helicobacter pylori associated with autoimmune thyroid disease in Iranian patients?