A 54-year-old man was seen in the clinic with the chief complaint of epigastric pain radiating to the left groin region and a predominant postprandial abdominal discomfort. Upon examination, a painless round mass with reduced mobility was felt in the left flank during deep palpation of the abdomen. His past medical history was irrelevant. Ultrasound and IV contrast-enhanced CT scan confirmed the presence of a large tumor and an exploratory laparotomy for removal of the tumor was performed. The microscopic examination of the specimen confirmed the primary diagnosis of retroperitoneal tumor (RPT) and identified it as an extragonadal germ cell tumor with a vestigial origin, which is a rare type affecting the kidney and adrenal gland. Primitive RPTs are histologically classified as mesenchymal and neuroectodermal or vestigial. These histological types are rarely found in surgical practice and are challenging to diagnose and treat due to the peculiarities of the site of origin where they develop. RPTs are extremely rare and approximately 80% are malignant and detected lately during the disease's course, commonly discovered in advanced stages of local or systemic evolution. Currently, surgical intervention remains the only effective method of treating these tumors.