The clinical case of a 65-year-old woman with an incidentally detected left-sided mass in the upper renal pole is presented. A functional adrenal tumor was excluded. The mass was removed retroperitoneoscopically. The perioperative period was uneventful. The histopathological examination revealed a heterotopic intrarenal adrenocortical oncocytoma. Adrenal oncocytic neoplasms are very rare, with, to the authors' knowledge, only 159 described cases so far. Most cases are non-functioning adenomas that can reach a considerable size. Only 10 heterotopic adrenal oncocytomas have been described (three retroperitoneal and seven intraspinal cases). Although the intrarenal adrenal rest is the most frequently appearing variant of adrenal heterotopia, to the best of our knowledge, this report is the first description of an intrarenally growing adrenocortical oncocytic adenoma. In addition to retroperitoneally located oncocytomas, this case could be interesting for urological practice because there are no diagnostic features which could provide a secure preoperative diagnosis of an adrenal oncocytic neoplasm and its malignant variant. Generally accepted indications for surgery of adrenal masses have to be respected. The definitive pathologic diagnosis is in most cases surprising because of its rarity. Benign adrenal oncocytic neoplasms do not require any adjuvant treatment. The oncocytic variant of adrenocortical carcinoma generally has a poor prognosis.