Because adrenal casts are rare condition, they are often misinterpreted and misdiagonosed. Here we report one case of epithelial retention cyst of the adrenal gland. This 63-year-old male patient was admitted due to abdominal distension and retroperitoneal huge cystic mass for 2 months. Gross examination revealed a huge unilocular cyst, measuring 18×16×12 cm in dimension. Within the wall, compresses adrenal gland was noted. Histologically, fibrous wall surrounded the adrenal parenchyme and cuboidal to low columnar cells lined the inner surface of the cyst. On the oasis of these findings, a diagnosis of adrenal cyst, epithelial retention cyst, was made. We reviewed literature of the adrenal cyst and discussed on the incidence, classification, pathogenesis, and pathologic findings.