Several studies report a higher rate of papillary thyroid carcinomas (PTC) in patients with Hashimoto thyroiditis (HT), indicating a possible correlation between the two diseases. We studied a group of 89 subjects undergoing surgery for thyroid carcinomas compared with a control group of 89 subjects operated on for normofunctioning goiter, and a second group of 47 patients undergoing total thyroidectomy for HT. Association with HT was found in 19 of the 71 PTC subjects (26.7%) and in 8 goiter patients (8.9%), which was a significant difference (P < 0.02). Thirteen of the HT patients, mostly with the nodular form, showed coexistent PTC (27.6%). HT and PTC coexisted in several morphological, immunohistochemical, and biomolecular aspects; increased incidence of PTC in HT patients might therefore indicate that HT is a precursor of thyroid cancer. Further studies are required, however, in order to confirm this hypothesis; until then, HT patients should undergo careful clinical and technical follow-up.