en Endocrinology Research (Original) <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><b><span style="color:black">Background:</span></b><span style="color:black"> Over the past few decades, numerous studies have been conducted to explore the association between blood groups and thyroid disorders. However, thus far, the findings of these studies have been contradictory. This investigation aims to examine the prevalence of different blood groups among patients with thyroid disorders.</span></span></span><br> <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><span style="color:black"></span></span></span><br> <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><b><span style="color:black">Material and Methods:</span></b><span style="color:black"> This study was conducted on 1880 patients who had thyroid disorders including hypothyroidism, hyperthyroidism, and thyroid nodules with or without thyroid dysfunction. These patients were referred to the Endocrine Clinic of Sari in 1400. We extracted and recorded demographic information, which included age, sex, weight, and height, presence of thyroid nodule in ultrasound, needle aspiration, and the patient&#39;s blood type.</span></span></span><br> <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><span style="color:black"></span></span></span><br> <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><b><span style="color:black">Results:</span></b><span style="color:black"> Out of a total of 1880 individuals, 221 individuals (11.8%) were normal, 278 individuals (14.8%) were hyperthyroidism, and 1381 individuals (73.5%) were hypothyroidism. Among the patients, 26.4% of the total subjects had blood group B, 9.8% had blood group AB, 22.3% had blood group A, and 41.4% had blood group O. Furthermore, 8.6% of these individuals were Rh-negative. There was no significant association between thyroid disorders and blood group (P=0.94) as well as Rh (P=0.34). In addition, there was no significant association between thyroid nodule and blood group (P=0.40) and Rh (P=0.17), although a significant relationship was found between nodule and thyroid function (P=0.00001). Also, a significant association between malignancy and thyroid function (P=0.00001).</span></span></span><br> <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><span lang="FA" dir="RTL" style="color:black"></span></span></span><br> <span style="font-size:12pt"><span new="" roman="" style="font-family:" times=""><b><span style="color:black">Conclusion:</span></b><span style="color:black"> Individuals with O blood type exhibited a higher frequency of thyroid dysfunction and thyroid cancer compared to those with other blood types.</span></span></span> ABO blood groups, Thyroid dysfunction, Hypothyroidism, Hyperthyroidism 13 20 http://tbsrj.mazums.ac.ir/browse.php?a_code=A-10-183-1&slc_lang=en&sid=1 Amirhossein Khoshgoeian w.amirhoseinkhoshgoeian@gmail.com 100319475328460031421 100319475328460031421 No Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran Zahra Hosseini-khah zahra_582005@yahoo.com 100319475328460031422 100319475328460031422 No Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran Zahra Kashi kashi_zahra@yahoo.com 100319475328460031423 100319475328460031423 No Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran Marzieh Movahedirad marziehmovahedi@gmail.com 100319475328460031424 100319475328460031424 No Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran Adele Bahar doctor_bahar2000@yahoo.com 100319475328460031425 100319475328460031425 Yes Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran