Background and objective: Thyroid disorders caused by blood transfusion in thalassemia patients could affect human health and growth, this study was conducted to determine the frequency of clinical and subclinical hypothyroidism in blood transfusion-dependent thalassemia patients in the city of Slemani, Kurdistan Region, Iraq. Methods: The current study is a retrospective cross-sectional study (comparative analysis) conducted in Slemani center for thalassemia patients and congenital blood, between December 2021 and July 2022. Participants included l07 thalassemia patients with medical records the sampling method was a convenience method. The data was collected through the review of patients' files and blood tests, including( thyroid hormones, hemoglobin level, serum ferritin level), with a questionnaire that was completed through an interview with the patients. Results: The results of thyroid function tests have shown that 21/107 pateints (19.6%) have hypothyroidism, 6 patients have overt hypothyroidism, and 15 patients have subclinical showed that 23/107 patients and 4/107 patients had hight and low levels,respectively, and there was statistically a significant difference in the average Thyroid stimulating hormone and serum thyroxin levels in two groups of hypothyroid and euthyroid patients and mean ferritine serum level between these two groups was 2166.7±2174.8 and 2068.37±1919.97 respictively ,which was not a statistically significant difference . Conclusion: Considering the high prevalence of hypothyroidism in thalassemia patients, measuring Thyroid stimulating hormone and thyroxin can be very important and vital in the initial screenings,effective treatment and follow-up of patients.