In a 45 years old women affected by Hashimoto's thyroiditis appeared a thyroid nodule that at the cytologic and than at the histologic examination proved to be a papillar carcinoma. Concerning this problem the authors make a thorough analysis of the literature. Regarding the possible associations between these two diseases, they observe how there is an extreme discordance of opinions on considering statistically significant the relationship between thyroid cancer and Hashimoto's thyroiditis. They make the hypothesis that the association of these two diseases is not casual: several etiological factors could be considered, but the chronic stimulus of TSH on the thyroid tissue affected by the autoimmune disease and progressively hypofunctioning, could be the main factor responsible for the development of the neoplasia. Then they give some advice to recognise patients at high risk for thyroid carcinoma. The patients at higher risk for thyroid cancer are those that present a single or prevalent nodule; the growth of a nodule on suppressive treatment with levothyroxine is also a negative prognostic index. Patients with an enlarged gland without nodules or with nodular goiter without a prevalent nodule are at low risk for cancer.