Summary Objective: Hashimoto's thyroiditis (HT) is an autoimmune inflammatory disorder. The purpose of this study was to determine the neutrophil-to-lymphocyte ratio (NLR), a novel marker of inflammation, in patients with HT and to compare these values with those from healthy subjects. Method: A total of 154 participants were included in the study, 90 HT patients and 64 healthy volunteers. Retrospectively, demographic and laboratory data of the subjects were obtained from our institution's database. Patients with active infection, diabetes mellitus, malignancy, other chronic inflammatory diseases, hematologic disorders and patients on aspirin or steroid treatment were excluded from the study. Values for complete blood count (CBC) and serum laboratory parameters of HT patients were the baseline values obtained at the time of HT diagnosis. Control subjects consisted of healthy volunteers who visited our institution for a routine check-up. Results: Age, gender and CBC parameters were not different between the HT group and the control group; however, the NLR of HT group (2.1 [1.3-5.8]) was significantly higher than the control group (1.9 [0.6-3.3]), p=0.04. Conclusion: Increased NLR may be useful as an indicator of the presence of HT, especially in complicated cases. NLR is inexpensive and easy to determine. Larger, prospective studies are required to determine its usefulness in assessing diagnostic potential and treatment outcomes in HT patients.