Carcinoid tumors have been reported in a wide range of organs but most frequently involve the gastrointestinal tract; however, duodenal carcinoid tumors are rare. We report a 50-year-old male patient complaining of multiple melenas for 3 wk. The panendoscopy and endoscopic retrograde cholangiopancreaticography revealed swelling accessory papilla with an ulcer. The biopsy taken showed a carcinoid tumor. The lesion was removed by wide resection. Patient was found to have an abnormal blood cell count during the follow-up period with elevated levels of hemoglobin and hematocrit of 21.2 g/dL and 63.5%, respectively, thrombocytosis of 501,000/microL, and leukocytosis of 20,410/microL. He was diagnosed as a polycythemia vera by a hematologist after further evaluation. He received periodic phlebotomy and hydroxyurea treatment. The response was good and his hematocrit was stabilized by periodic phlebotomy in the range of 44-49% during the last 2 years. The possible origin of UGI bleeding by a duodenal carcinoid tumor, although rare, should be considered. There has been one case report of a duodenal carcinoid tumor that involved accessory papilla of the pancreas divisum and one case report of metastatic carcinoid tumor associated with polycythemia vera. It is different in our patient as compared with the latter report, which mentioned a polycythemia vera patient who was found to have a metastatic carcinoid in the 17 years follow-up period. Chemotherapy had been given before the carcinoid tumor was revealed. Our patient had no previous chemotherapy for polycythemia vera before he was found to have duodenal carcinoid tumor; this excludes the possibility of chemotherapy induced carcinoid tumor, although it had been suspected in the previous report. In our patient, the existence of both diseases may be by predisposition of each other since both diseases have an increased incidence of other neoplasm, or they may be coexistent incidentally.