© 2021 AACEObjective: This study evaluated the impact of chronic lymphocytic thyroiditis (CLT) on clinicopathologic parameters, prognostic outcome, and initial treatment responses in patients with papillary thyroid cancer (PTC). Methods: A retrospective review was conducted of 1409 patients with PTC, comprising 443 patients with pathology-proven PTC with CLT and 447 patients with PTC without CLT. Results: The median follow-up time was 58 months (range, 8-380 months), and the median age at the time of diagnosis was 43 years. The age at diagnosis was significantly lower in patients with CLT than in those without CLT (42 years vs 45 years, respectively; P = .001). The preoperative thyroid-stimulating hormone level was found to be significantly higher in patients with CLT than in those without CLT (1.71 mIU/L vs 1.28 mIU/L, respectively; P < .001). Multifocality and capsular, lymphovascular, and perineural invasion were detected at a higher rate in the group with CLT than in the group without CLT (P = .015, P = .024, P = .004, and P = .039, respectively). No difference was found between the 2 groups in terms of tumor size, bilaterality, extrathyroidal invasion, lymph node metastasis, disease stage, or response to treatment (P > .05). Conclusion: The results of the present study demonstrated that the coexistence of PTC and CLT is very frequent. Patients with the coexistence of PTC and CLT were diagnosed at a younger age, and the thyroid-stimulating hormone level was higher in these patients. Contrary to previous studies, no positive effect of the CLT and PTC combination was detected on any clinicopathologic factor. In addition, lymphovascular and perineural invasions, which had negative effects on prognosis, were more common in the group with CLT.