Out of 35 consecutive patients with decreased plasma-cobalamin 22 had newly diagnosed overt pernicious anemia (PA) six of which had a known history of thyroid disease. At referral, 5 of these 6 were thyroid peroxidase antibody (TPOAb)-positive and 2 were thyroglobulin antibody (TgAb)-positive, while none were thyroid stimulating antibody (TSAb)-positive (an overall autoantibody appearance of 83.3%). Fifty percent of the 22 patients had TPOAb and 13.6% had TgAb compared to 18.2% and 4.5%, respectively in sex and age matched healthy controls. Six PA-patients without a history of thyroid disease had thyroid autoantibodies and another patient seroconverted within the first year during treatment with cyanocobalamin. Measurements of serum concentrations of thyroid hormones and thyroid stimulating hormone were performed during the first year of treatment with cyanocobalamin. Two cases of subclinical myxoedema were found among PA-patients and another case was found among patients with latent PA. The female:male ratio of thyroid disease among PA-patients and among thyroid autoantibody-positive PA-patients was interestingly found to be 1:1. Treatment with cyanocobalamin did not have any systematic effect on thyroid function. Routine screening for thyroid function and thyroid autoantibodies in patients with latent or overt PA is recommended.