The patient was a 40-year-old male of Bulgarian nationality with a personal history of gastro-oesophageal reflux and incompetent cardia, not previously operated on or transfused, employed as a metal carpenter, smoker of 15-20 cig/day and a moderate ex-drinker until 4 years ago. His family history included his mother, father and a brother with nephrolithiasis. He had been seen 21 days before admission for pain in the right flank with irradiation towards the ipsilateral testicle, which was classified as probable renal colic and treated with analgesia, with favourable evolution; he subsequently started again with similar symptoms accompanied by nausea without thermometric fever or micturition syndrome; he did not report loss of appetite or weight. He returned to the emergency department where an abdominal ultrasound scan was performed describing the presence of grade II/IV hydronephrosis and a 6-7 cm mass in the right reteroperitoneum, for which he was admitted for further study. The patient reported pain in the right renal flank/fossa radiating to the ipsilateral teste without nausea, vomiting or thermometric fever. Examination revealed only positive right renal suction. ECG in sinus rhythm at 76 bpm; chest X-ray with no significant pathological alterations. Blood tests showed fibrinogen 478 mg/dL (150-450), ESR21 mm/hour (2-15), urea 52 mg/dL (10-50), creatinine 1.4 mg/dL (0.6-1.2), LDH 446 U/L (0-288), human gonadotropinacorionic acid 7 UI/L (0-5) and alpha-fetoprotein 2.2 kU/L (0.5-7). An abdominopelvic CT scan was performed showing a single "soft tissue" mass of rounded morphology (7 x 5.5 cm) with a uniform density and a focal area of lesser attenuation that "encompasses" the inferior vena cava and the right ureter with grade 2 hydronephrosis; the lesion is well defined and no adenopathy or accompanying satellite lesions can be seen in the middle retroperitoneum (between the aorta and the inferior vena cava). Urgent referral was made to the Urology Department, which performed a right nephrostomy. A trucut biopsy of the retroperitoneal mass was performed under ultrasound guidance and the specimen was sent to anatomical pathology, which reported it as a neoformation consisting of large cells arranged in nests, with little cohesion and a cytoplasm of imprecise limits, generally finely vacuolated, The nuclei are rounded or cleaved, with a large nucleolus and the cells are arranged in nuclei and are surrounded by a large number of small lymphoid cells, corresponding to mature lymphocytes. The tumour cells are positive for C-Kit and are compatible with a classic seminoma-type germinal tumour. In view of this, a testicular ultrasound scan was performed, showing a 16 mm nodular-ovoid, isodense lesion with a peripheral hypodense halo, located in the upper half and subcapsular anteriorly, as well as another small hyperechoic nodule of approximately 5 mm, compatible with a right testicular tumour. He was subsequently referred to the Urology Department, after consultation with Oncology, to perform an orchiectomy and subsequently undergo chemotherapy cycles in the Oncology Department.