Adrenocortical oncocytic neoplasm arising in ectopic adrenal tissue is a rare finding and presents as a unique diagnostic challenge. We report a case of a 26-year-old female who presented with vague left-sided abdominal pain and a large left retroperitoneal mass. She underwent exploratory laparotomy and resection of the mass and was diagnosed with extra-adrenal adrenocortical oncocytic carcinoma.