Abstract Background South Korea has the highest incidence of thyroid cancer worldwide, raising questions regarding the possibility of overdiagnosis. Examining the factors affecting thyroid cancer screening is crucial in elucidating the reasons for this unusually high incidence of thyroid cancer. Therefore, in the present study, we investigated the association between breast cancer screening and thyroid cancer screening to determine the potential role of breast cancer screening in the overdiagnosis of thyroid cancer in South Korea. Methods We analyzed the data of women aged > 30 years who were enrolled in the 2014 Korean National Cancer Screening Survey. Self-reported breast cancer screening behavior was categorized as follows: no screening, mammography only, ultrasonography only, and both ultrasonography and mammography. Thyroid cancer screening behavior was categorized as follows: those who had or had not undergone ultrasonography screening. Logistic regression analysis was used to examine the associations between breast and thyroid cancer screening behaviors. Results Of the 2270 participants, a total of 569 (25.1%) were screened for thyroid cancer. Those who underwent only mammography, only ultrasonography, or both mammography and ultrasonography were more likely to be screened for thyroid cancer than those who did not undergo breast cancer screening (odds ratio [OR]: 1.47, 95% confidence interval [CI] 1.06–2.04; OR 2.71, 95% CI 1.83–4.02; OR 2.75, 95% CI 1.99–3.80, respectively). Conclusions Our findings indicate that thyroid cancer screening in Korea is likely to be performed on an opportunistic basis. Therefore, a nationwide public health and medical initiative is needed to curb the unnecessary use of thyroid screening in the asymptomatic general population.