BACKGROUND: Autoimmune thyroid disease (AITD) often coexists with pernicious anemia (PA) among whites. The study aimed to determine thyroid autoimmunity in Chinese patients with PA. METHODS: From the data of a hospital-based longitudinal study of Chinese PA patients (1994-2007), those with complete information of antibodies to thyroid peroxidase (TPO), thyroglobulin (Tg), and gastric parietal cell; serum thyroid-stimulating hormone and free thyroxine; gastric mucosal histology; and family history of AITD were analyzed. RESULTS: Among 126 Chinese PA patients, 44% had TPO/Tg antibodies and 13.5% AITD. TPO/Tg antibodies occurred in 33% (16 of 49) of male and 52% (40 of 77) of female patients (P = 0.034). Graves disease (8 patients) tended to antedate PA and was associated with no or low titers of TPO/Tg antibodies. Primary hypothyroidism (9 patients) developed during follow-up and was associated with high TPO/Tg antibody titers. The TPO/Tg antibodies did not affect the clinical course of PA but was associated with an enhanced risk of developing AITD and vitiligo. Overall, AITD (before and after PA) occurred in 23% (13 of 56) and 5.7% (4 of 70) of PA patients with and without antibodies (P = 004). During follow-up (mean duration of 75.24 +/- 46.39 months), 10 patients developed AITD-7 new onset of hypothyroidism and 3 progression/relapse of prior AITD. Logistic regression analysis of presenting features of PA revealed 2 independent factors for AITD development during follow-up-presence of thyroid antibodies (odds ratio 20.2, 95% confidence interval 1.8-223) and history of prior AITD (odds ratio 39.8, 95% confidence interval 2.3-679). CONCLUSION: It is recommended to screen thyroid antibodies and monitor thyroid function during follow-up.