Graves' disease (GD) is the most common cause of hyperthyroidism in iodine-replete populations. It is an autoimmune disease caused by autoantibodies to the TSHR (TRAb). Although the diagnostic is mainly clinical, measuring TRAb improves accuracy and provides valuable prognostic information. The aim of this study was to compare the performance of two of the most widely used immunoassays i.e., EliA™ anti-TSH-R and Elecsys® anti-TSH-R. We have carried out a comparative study measuring TRAb by the two immunoassays in consecutive sera samples referred to the laboratory for TRAb measurement. Autoantibodies were measured in all samples in parallel by the two techniques. The two techniques were highly concordant as demonstrated by a Cohen's kappa of 0.82. At the manufacturer recommended cut-off, sensitivity of Elecsys® TRAb test was higher (100% vs. 96.6%), while specificity of the EliA™ TRAb test was higher (99.4% vs. 95.3%). In most patients TRAb are detected by any of two tests which are both well suited for Clinical Laboratories use. However, a higher specificity may constitute an advantage for measurement used not for screening but for diagnostic purposes, as anti-TSH-R is.