en هماتولوژی و آنکولوژی Hematology & Oncology پژوهشي Research <div style="text-align: justify;"><strong>Background:</strong> The incidence of thyroid cancer (TC) is increasing globally. This study examined the incidence of TC in Mazandaran Province, Northern Iran, from 2016 to 2020.<br> <strong>Methods: </strong>We conducted a cross-sectional study using data from the Mazandaran cancer registry. Age-standardized incidence rates (ASIRs) and the average annual percentage change (AAPC) with 95% confidence intervals (CI) were calculated using the Joinpoint Regression Program software, version 4.9.0.0.<br> <strong>Results:</strong> The number of cases rose by 90.9%, increasing from 253 in 2016 to 483 in 2020. The ASIR increased from 6.43 to 11.14 per 100,000. While the overall trend was not statistically significant (AAPC=14.5%, P=0.08), a significant increase was observed in males (AAPC=19.8%, P<0.05). The incidence rate in women was approximately five times that of men (15.14 vs 3.06 per 100,000, P<0.001) and was more common in urban areas.. Most new cases (over 80%) occurred in the 25&ndash;59 age group.<br> <strong>Conclusion:</strong> TC incidence has risen substantially in Mazandaran Province, particularly among women and urban residents. These findings highlight the need for further investigation into underlying causes and preventive measures.</div> Thyroid cancer (TR), Incidence, Mazandaran,Trends, Epidemiology 107 116 http://rmm.mazums.ac.ir/browse.php?a_code=A-10-777-2&slc_lang=en&sid=1 Elahe Mahmoodi mahmodi85@yahoo.com 100319475328460012947 100319475328460012947 No Mazandaran Cancer Registry Research Center, Mazandaran University of Medical Sciences, Sari, Iran. Akbar Hedayatizadeh-Omran akbar_hedayati@yahoo.com 100319475328460012948 100319475328460012948 Yes Gastrointestinal Cancer Research Center, Non-communicable Diseases Institute, Mazandaran University of Medical Sciences, Sari, Iran. Mahmood Moosazadeh mmoosazadeh1351@gmail.com 100319475328460012949 100319475328460012949 No Gastrointestinal Cancer Research Center, Non-communicable Diseases Institute, Mazandaran University of Medical Sciences, Sari, Iran. Reza Alizadeh-Navaei reza_nava@yahoo.com 100319475328460012950 100319475328460012950 No Gastrointestinal Cancer Research Center, Non-communicable Diseases Institute, Mazandaran University of Medical Sciences, Sari, Iran. Toktamosadat Mohammadi toktammohammadi@yahoo.com 100319475328460012951 100319475328460012951 No Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. Zahra Kashi kashi_zahra@yahoo.com 100319475328460012952 100319475328460012952 No Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran.