Hemoptysis is a major reason for emergency department (ED) visits. Catamenial hemoptysis (CH), a rare condition of thoracic endometriosis, can cause recurrent hemoptysis but is difficult to diagnose in the ED due to the scarcity of cases and nonspecific clinical findings. We report a case of a 26-year-old woman who presented to the ED with recurrent hemoptysis since 2 years without a definite cause. Her vital signs and blood test findings were unremarkable. Chest computed tomography (CT) did not show any specific lesions other than a non-specific ground-glass opacity pattern in her right lung. She was on day 4 of her menstrual cycle and her hemoptysis frequently occurred during menstruation. Although there was no histological confirmation, based on her history of hemoptysis during menstruation and no other cause of the hemoptysis, the patient was tentatively diagnosed with CH and was administered gonadotropin-releasing hormone. She had no recurrence of hemoptysis for 3 months. While CH is difficult to diagnose in the ED, the patient's recurrent hemoptysis related to menstruation was a clue to the presence of CH. Therefore, physicians should determine the relationship between hemoptysis and menstruation for women of childbearing age presenting with repeated hemoptysis without a definite cause.