A patient with an incidentally diagnosed adrenal ganglioneuroma is reported. A 37-year-old man who underwent abdominal computed tomography (CT) in the course of evaluating liver dysfunction was found to have a right adrenal tumor. Laboratory data including results of endocrinologic tests were normal except for a slight elevation of plasma aldosterone. With a preoperative diagnosis of non-functioning right adrenal tumor, resection was performed. The tumor specimen was noncystic weighing 150 g and measuring 10 x 8 x 3 cm. The histopathologic diagnosis was ganglioneuroma originating from the adrenal gland. Adrenal ganglioneuroma is relatively rare, 147 cases including ours have been reported in Japan. Increasing numbers of these tumors are being found incidentally by ultrasonography or CT. Ganglioneuroma is a benign tumor, and disagreement exists concerning diagnosis and indications for surgery.