BACKGROUND/AIM: The telomerase reverse transcriptase (TERT) promoter has a regulatory single nucleotide polymorphism (rSNP), rs2853669, and occasionally shows point mutations C228T and C250T. Although C228T and C250T have been well examined to increase TERT promoter activity and are known as risk factors for thyroid carcinoma, the significance of rs2853669 has not been well investigated. This study aimed to clarify the influence of rs2853669 on TERT promoter activity in thyroid carcinoma cells. MATERIALS: Seven of 8 examined thyroid cell lines had rs2853669, 5 had C228T, and 1 had C250T. RESULTS: Three papillary thyroid carcinoma cell lines, harboring both rs2853669 and C228T, showed higher TERT mRNA expression on real-time PCR than the other cell lines. Anaplastic thyroid carcinoma cell lines, in contrast, showed variable TERT mRNA expression depending on the combination of rs2853669, C228T, and C250T. Luciferase assays, performed to compare the influences of rs2853669, C228T, and C250T on TERT promoter activity in thyroid carcinoma, showed that rs2853669, as well as C228T, increased the promoter activity, and the combination of rs2853669 and C228T increased the promoter activity even more strongly than C228T alone. CONCLUSION: We conclude that the presence of rs2853669 within the TERT promoter could be as significant as the C228T mutation in thyroid carcinoma.