Graves' disease (GD) is the only autoimmune disease where autoantibodies stimulate the target organs. Among the most common clinical manifestations are hyperthyroidism and orbitopathy (GO). To ensure the diagnosis of autoimmune hyperthyroidism, activity of TSH receptor autoantibodies (TRAb) should be determined. Because of their significantly improved sensitivity and equal specificity, second-generation TRAb assays (activity given in IU/l) should be preferred over first-generation assays (activity given in U/l). During follow-up of antithyroid drug therapy it is possible to predict outcome for some patients with high chances if TRAb levels are high. On this basis, thyreoablative treatment (operation or radioiodine) can already be indicated before the 1st year of antithyroid drug treatment has passed. If TRAb antibody titers are > 10 IU/l, it is possible to predict outcome as early as 6 months after initiation of antithyroid drug therapy. Below a certain threshold, depending on the time point of measurement, no representative risk analyses are available for TRAbs. TRAb measurement is also helpful to determine the course of GO. This may guide the physician through crucial treatment decisions, especially if the patient is at risk of deterioration.