Objective: Thyroid nodules are highly prevalent and a common clinical problem worldwide. How to identify the nature of a nodule is a major concern of clinicians. Fine needle aspiration cytology (FNAC) has an established role and is well-utilized in nodule management. However, the unsatisfactory nondiagnostic and indeterminate rates limit its usage and lead to some unnecessary surgery. Hashimoto thyroiditis (HT) is prevalently found concurrent with thyroid nodules. Whether HT can influence the accuracy of cytopathological diagnosis of nodules is still controversial. Methods: We collected medical records of 1,063 patients with thyroid nodules who had done FNAC in our hospital from 2015 to 2016. Thyroid function, anti-thyroid autoantibody levels, thyroid ultrasound records, and cytological and histopathological results of nodules were reviewed to analyze the impact of HT on FNAC outcome. Results: A total of 1,063 patients with an average age of 44 ± 13 years old were retrospectively reviewed for pathological and clinical data. Patients with different cytological diagnoses had comparable positive rates of anti-thyroid autoantibodies. One hundred patients were confirmed to have concurrent HT by histopathology after surgery. The overall nondiagnostic and indeterminate cytology rates were 11.9% and 25% respectively. No statistical difference was found either in the rate of a nondiagnostic cytology results or in the rate of indeterminate cytology results between patients with positive anti-thyroid autoantibodies and patients with negative test for anti-thyroid autoantibodies (P > 0.05). The same was true between patients with histopathologically confirmed HT and HT-negative ones (P > 0.05). Conclusions: The presence of concurrent HT, whether clinically implied with positive anti-thyroid autoantibodies or pathologically confirmed, is unlikely to predispose an FNAC diagnosis of thyroid nodules to be non-diagnostic or indeterminate. [ABSTRACT FROM AUTHOR]