A 68-year-old woman with a history of arterial hypertension and hypothyroidism came to the emergency department with acute pain in the left hypochondrium, with no history of trauma, of a constant nature, radiating to the epigastrium with approximately 3 hours of evolution, accompanied by dizziness and weakness. Physical examination revealed hypotension and tachycardia that was maintained despite the administration of intravenous fluids; the abdomen was painful, predominantly in the hypochondrium and left lumbar fossa, with no signs of peritoneal irritation. Ultrasound and computed tomography (CT) showed the presence of a rounded retroperitoneal tumour measuring approximately 10 x 12 cm in front of the upper pole of the left kidney, vascularised, with irregular contrast uptake and small calcifications inside; in addition, there was an increase in the density of the retroperitoneal space compatible with bleeding. With the aforementioned findings, surgery was performed, revealing a large left retroperitoneal haematoma extending to the midline and the left iliac fossa and a tumour approximately 12 cm in diameter above the upper pole of the left kidney, encapsulated, with active bleeding due to a fissure in it, which was removed, preserving part of the adrenal gland and the left kidney. The evolution is satisfactory. Subsequent evaluation revealed the absence of arterial hypertension and abdominal ultrasound showed no pathological findings. The biopsy described a nodular tumour 10 cm in diameter and weighing 457 grams, reddish in colour with a yellowish peripheral margin, with a microscopic diagnosis of adrenal endothelial pseudocyst.