Cancer and autoimmune diseases are often associated in the same individual. The functional link between the immune system and cancer development is only partially known. Even though the immune system can control the development of cancer through immune surveillance, cancer cell can escape it. It is debated whether autoimmune diseases have to be regarded as a cancer cause or its consequence. In particular, the association between autoimmune thyroiditis and thyroid cancer (TC; especially papillary carcinoma) is a fascinating model of this complex relationship. In this review, we present data reported in literature about autoimmune thyroiditis and papillary TC, and on the basis of available data, we try to clarify the present knowledge.