We report a case of non-functioning retroperitoneal paraganglioma detected incidentally by health examination in a 60-year-old female without any clinical manifestation. She was admitted to our hospital for the purpose of evaluation of a renal mass detected by ultrasound sonography. Computed tomography, magnetic resonance imaging and angiography revealed the heterogeneously-enhanced 10 x 10 cm mass in the left retroperitoneal space without any distant metastasis. It was suspected to be a renal cell carcinoma. All laboratory data, including those from endocrinological examinations, were within normal ranges. Radical nephrectomy was performed to resect en bloc the mass and the left kidney. The pathological and immunohistochemical examinations of the mass which was completely separated from the kidney and the adrenal gland, showed characteristic features of paraganglioma with vascular and capsular invasion, with a final clinical diagnosis of the pathologically-malignant non-functioning paraganglioma occurring between the left kidney and the adrenal gland.