It has been reported that prostaglandin I2, such as epoprostenol, develops Grave's disease. A 34-year-old woman was diagnosed with idiopathic pulmonary arterial hypertension and started receiving continuous intravenous epoprostenol. Three years after starting epoprostenol, she started complaining of neck swelling and was diagnosed with Grave’s disease. Thyroid function was controlled by thiamazole and levothyroxine. Nevertheless, her thyroid gland enlargement worsened as epoprostenol dose was titrated. After 23 years of treatment with epoprostenol, she suddenly experienced respiratory failure with a giant goiter leading to airway stenosis and passed away. The autopsy confirmed a giant goiter associated with hyperthyroidism and airway stenosis. We experienced a case of idiopathic pulmonary hypertension with a giant goiter and airway stenosis after long-term intravenous epoprostenol therapy.