We report two cases of retroperitoneal functioning paraganglioma. Case 1: A 52-year-old male patient was admitted to our hospital for further examination of pulsating abdominal pain with chest pain and headache. Overfist-size smooth-surfaced hard mass was palpated at the right upper abdominal quadrant. Catecholamine levels in serum and urine showed marked elevation. Computed tomographic (CT) scan, magnetic resonance imaging (MRI) and angiography revealed a large tumor between the right kidney and aorta. He underwent surgical removal of the tumor and histological examination revealed paraganglioma. His chief complaints disappeared postoperatively. Case 2: A 68-year-old female patient was admitted to our hospital for control of diabetes. An abnormal mass was shown ultrasonically at the left renal region by routine screening examination. A marked increase of noradrenaline in serum and urine was observed. Abdominal CT scan, MRI and angiography revealed a retroperitoneal tumor which was located adjoining to the lower pole of the left kidney. The tumor was removed transabdominally. Histopathological studies showed paraganglioma. After the operation her blood sugar and noradrenaline levels decreased to the normal range.