AIM: This study aimed to assess the trends in the incidence of thyroid cancer in Incheon Province, South Korea, from 2004 to 2013 and to identify its association with thyroid cancer screening. METHODS: We evaluated randomly sampled data of 10% of thyroid cancer patients collected between 2004 and 2013 from the Incheon Cancer Registry, Incheon, South Korea. The expected annual incidence rates of thyroid cancer from 2004 to 2013 were calculated, and the trends in annual incidence change were assessed using a Poisson regression model. In addition, the annual proportion change in the thyroid cancer population according to the detection method and tumor size was also calculated by evaluating the linear-by-linear association. RESULTS: The average expected prevalence of thyroid cancer was 30 per 100,000 individuals from 2004 to 2013. The expected annual incidence of thyroid cancer per 100,000 individuals increased from 7 in 2004 to 49 in 2013, with an annual 1.25-fold difference (p < 0.001). Screening helped improve the detection of thyroid cancer annually, with the proportion increasing by screening detection (p < 0.001). Majority (54%) of the tumors were small (< 10 mm) and their detection rate increased from 2004 to 2013 (p < 0.001). CONCLUSIONS: The incidence of thyroid cancer has increased from 2004 to 2013 in Incheon Province, South Korea, with the increase being most significant for small tumors. These findings indicate that the increased incidence is primarily due to the widespread use of screening and not an actual increase in clinically significant thyroid cancer.