Cystic nephroma(CN) is a rare benign cystic renal tumor, which only recently has been recognized as an exclusively adult lesion. CN presents after age 30 and affects primarily reproductive age to early menopausal women. Although an aggressive behavior has been reported in very few cases, CN is considered as a benign lesion and surgical excision is curative. We report on a case of CN in a 31-year-old woman who presented with an incidentally detected renal tumor. The patient has had no evidence of disease 5 years after radical nephrectomy.