A 87-year-old man was diagnosed with prostate cancer (cT2aN0M0 Gleason score 4＋4 with initial prostate specific antigen of 23.4 ng/ml). Prostate cancer was treated with combined androgen blockade (goserelin acetate plus flutamide). He was administered goserelin acetate depot injection without any complications as an outpatient. However, 5 hours after he left the hospital, he came back to the hospital, complaining of lower abdominal pain. Abdominal computed tomography revealed a giant subcutaneous hematoma in the lower abdomen. Hemoglobin was 6.9 g/dl and blood pressure was lower than 80 mmHg. He was admitted and given a blood transfusion. Because of pre-disseminated intravascular coagulation score 6, it was hard to antagonize warfarin by Vitamin K (he had taken warfarin because of atrial fibrillation). Arteriography was performed and injury to a branch of the lower epigastric artery was found. Transcatheter arterial embolization was performed at the same time. Injecting goserelin acetate may cause severe arterial injury.