A 58-year-old woman was referred to our outpatient clinic for further examination of a mass detected in the right kidney on follow-up ultrasonography performed for active surveillance of right ovarian cancer. Ultrasonography and computed tomography showed a cyst (diameter, 30 mm) with an irregular wall in the middle of the right kidney. Right nephrectomy was performed since malignancy was suspected. Histological findings of the mass indicated cholesterol granuloma. Although cholesterol granulomas in the middle ear have been frequently reported, those in other organs have been reported in few studies. In this patient, the cholesterol granuloma could be barely distinguished from the cancer by using imaging techniques.