Background: Incidental thyroid nodules (ITN) are defined as newly identified thyroid nodules encountered during imaging study. In practice, low-dose chest CT for screening of lung cancer often detects ITN. We investigated the prevalence and clinical significance of ITN. Methods: We retrospectively reviewed the medical records of all patients undergoing low-dose chest CT without previous thyroid disease during the period from Mar 2009 to Feb 2012 at Jeju national university hospital. The clinical characteristics, outcomes, and the CT findings were analyzed. Results: Among 1941 patients undergoing low-dose chest CT, 55 (2.8%) showed ITN. Seven (12.7%) of those were proven to have malignancy. The positive and negative predictive value of low-dose chest CT for detection of incidental malignancy in the thyroid were 12.7% and 99.3%, respectively. The considerable factors for the low-dose chest CT featuring of malignancy were mean attenuation value more than 55 and densely calcification (respectively, p=0.036 and p=0.048). Sex, age, location of nodule, longest diameter, AP/T ratio, margin, low density, any punctuate calcifications, and thyroid enlargements showed no benefits discriminating benign and malignant thyroid nodules. In multivariable analyses, only the mean attenuation value above 55 showed a statistical significance (p=0.048). Conclusion: For patients undergoing low-dose chest CT for screening of lung cancer, in addition to pulmonary lesions, careful assessment for thyroid glands might give additional benefits on the screening of incidental thyroid malignancies.