A 79-year-old male was referred to the Department of Gastroenterology in our hospital due to a large palpable abdominal mass, with the suspicion of a gastrointestinal stromal tumor. An abdominal computed tomographic (CT) scan revealed a huge mass of 270×208×144 mm which occupied the entire pelvic cavity. Since the specimens obtained by an endoscopic ultrasound-guided fine-needle aspiration via lower intestinal tract revealed a Gleason score 4＋4 prostate adenocarcinoma, he was then referred to our department. Prostate specific antigen (PSA) was elevated to 3,087 ng/ml, and positron emission tomography-CT revealed right obturator lymph node metastasis and bone metastasis of the left 5th rib. Degarelix was administered as an androgen deprivation therapy, and the PSA level had decreased to 62.4 ng/ml one month later. At the last follow-up, the PSA level was 0.67 ng/ml and the tumorsize had decreased to 88×83×110 mm. Next, we conducted a follow-up survey by mail of 20 reported Japanese cases of a giant prostate carcinoma, and data on 17 cases were available for analysis. In the total of 18 cases, including the present case, with a median follow-up time of 26 months, the 2-year overall survival rate was 85.7% for patients without metastasis, and 65.6% forthose with metastasis.