Antibodies to TSH receptors (TRAb) have great pathogenetic importance in the development and maintenance of hyperthyroidism in Graves' disease (GD). Measurement of their serum level could be of diagnostic and prognostic importance in autoimmune hyperthyroidism and in monitoring the efficiency of thyrosuppressive drug (TSD) treatment in GD. The aim of our study was to assess the sensitivity (SN), specificity (SP), positive predictive value (PPV) and negative predictive value (NPV) of the TRAb assay in confirming the diagnosis and to define its prognostic value for remission duration in GD patients at the end of TSD treatment with thionamide derivatives, propylthiouracil or methimazole. We studied 99 patients, 65 female, 34 male, 18-76 years old; 52 GD patients and 47 as control group. We have studied frequency of relapses and remission duration in GD patients by a 2nd generation serum TRAb commercial kit. Our results showed that, the SN, SP, PPV and NPV of the TRAb test were 100%, 97%, 98% and 100%, respectively. Remission duration after TSD treatment was longer and relapses were fewer in GD patients with lower levels of TRAb before (P<0.01) and at the end of TSD treatment (P<0.05). In conclusion, our results suggest that serum TRAb is very sensitive and specific for confirming the diagnosis of GD. TRAb levels at the beginning of TSD treatment, above 5 IU/L gives 18% greater chance, and above 15 IU/L, 36% greater chance for remission, shorter than 6 months.