No consensus exists on the association between Hashimoto’s thyroiditis and papillary thyroid carcinoma (PTC), which is the most prevalent form of thyroid cancer, comprising about 80% of all diagnosed thyroid cancers. Hashimoto’s thyroiditis (chronic lymphocytic thyroiditis) is a well-defined clinico-pathological entity, and its incidence has increased over the past 50 years. It is characterized by hypothyroidism, the presence of serum anti-thyroglobulin and anti-peroxidase antibodies, and widespread lymphocytic infiltration with depletion of follicular cells. In addition to the classical Hashimoto’s thyroiditis, recent studies have proposed that IgG4-related thyroiditis may be considered as a variant of the disease. Hashimoto’s thyroiditis has shown a wide range of occurrence from 5% to 85% in thyroid specimens resected for PTC. The association between Hashimoto’s thyroiditis and PTC has been a subject of long and ongoing debate. In addition, the clinico-pathological characteristics of PTC with concomitant Hashimoto’s thyroiditis have not been definitively proposed. As the incidence of Hashimoto’s thyroiditis is higher in PTC patients, careful clinical monitoring of patients with Hashimoto’s thyroiditis and meticulous histopathological examination of surgical specimens from these patients are required. The PTCs with Hashimoto’s thyroiditis are characterized by female predominance, multi-focality, no extra-thyroidal extension, no lymph node metastasis, and better recurrence-free survival outcomes. Occurrence of Hashimoto’s thyroiditis with PTC is not related to the age of the patient or the size of the tumor. This chapter aims at clarifying the relationship between Hashimoto’s thyroiditis (histologically-proven) and PTC and identifying the clinico-pathological features of PTC with co-existent Hashimoto’s thyroiditis.