Autoimmune phenomena are frequently associated with differentiated thyroid carcinomas. However, the significance of thyroid gland autoimmune aggression on the outcome of these patients is still controversial. To address this issue, we studied 173 patients (123 with papillary and 50 with follicular carcinomas) who underwent surgery complemented by radioiodine ablation and followed up for 0.5-29 (6 +/- 5.76) years. Analysis of the prognostic factors revealed that higher age, male gender, larger nodule size, follicular tumors, presence of metastases at diagnosis, grade of differentiation, and stage correlated positively with the occurrence of death, metastasis and/or recurrence, while the presence of antibodies and the previous history of autoimmune disease correlated negatively with these events. Long distant metastases increased the odds for a lower disease-free rate for patients with papillary (8.366 times) and follicular (7.373 times) carcinoma. However, univariate and multivariate analysis failed to demonstrate that neck node involvement could influence the outcome for patients with well-differentiated thyroid carcinoma. The odds for patients with previous history of thyroid autoimmune disease (p < 0.02) or with thyroid autoantibodies (p < 0.001) to have a worse outcome were lower than for patients with no evidence of autoimmune activity, suggesting that autoimmune activity against the gland may exert a protective effect on the outcome of differentiated thyroid carcinoma patients.o TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE AGOSTO DE 2015.135491495