Periadrenal retroperitoneal tumors are frequently misdiagnosed as adrenal tumors because of its rarity and anatomical vicinity. Thus, there are only very few cases reported and little information available in the literature. Preoperative diagnoses of theses tumors are challenging. The definitive diagnosis is based on postoperative pathological findings. We report two cases of periadrenal retroperitoneal tumors that mimicked adrenal neoplasms. Final diagnoses were mature cystic teratoma and papillary renal carcinoma, respectively. Although periadrenal retroperitoneal tumors are rare, it should be considered in the differential diagnosis of adrenal incidentalomas.