A rare case of retroperitoneal ganglioneuroma incidentally found during an annual health examination is presented. The patient was an asymptomatic female, age 26. Physical examination and routine laboratory studies gave normal results. The plasma concentrations and 24-h urinary excretion of catecholamine and its metabolites were within the normal range. The patient was diagnosed as having a left supra-renal mass (6.3 x 3.6 cm) by abdominal ultrasonography, although by image diagnosis the paraadrenal mass could not be discriminated from an adrenal tumor. Operation was performed under the suspicion of a nonfunctioning adrenal tumor. The tumor removed was 8 x 6 x 4 cm, 98 g and was encapsulated. Histopathological diagnosis of retroperitoneal ganglioneuroma was confirmed. Forty-one cases of retroperitoneal ganglioneuroma in the Japanese literature including the present case are reviewed.