Objective The recurrence rate associated with antithyroid drug (ATD) treatment for Graves' disease (GD) is high compared with that for radioiodine therapy or surgery. It is important to identify patients in whom remission is unlikely, so that they are not given treatment that is destined to fail. The objective of this study was thus to evaluate factors influencing the prognosis of GD patients treated with ATDs. Patients One hundred and sixty-one patients were divided into two groups: 100 patients who could not discontinue ATDs for eight years or more (refractory group) and 61 patients who achieved remission within eight years after starting ATD treatment (nonrefractory group). The groups were compared in terms of age, thyroid function and thyroid-related autoantibodies at diagnosis, and the durations to the recovery of thyroid function and thyroid-related autoantibodies. Results The baseline levels of free triiodothyronine (T3), free thyroxine (T4), thyroid-stimulating antibodies (TSAbs) and thyroid-stimulating hormone (TSH) receptor antibodies (TRAbs) were high, and the age at diagnosis and the baseline level of thyroglobulin autoantibodies (TgAbs) were low in the refractory group compared with those in the nonrefractory group. The durations to the recovery of TSH, free T4, TRAb and TSAb levels were longer in the refractory group than in the nonrefractory group. No significant difference was observed with regard to thyroid peroxidase autoantibodies. Conclusion We compared the clinical features of these two groups in order to identify factors influencing the prognosis of GD patients treated with ATDs. A low baseline level of TgAbs is associated with the refractoriness of GD to ATD treatment.