A 46 year old woman, hysterectomised for leiomyomas, came to the emergency department for intense pain in the left renal fossa, general malaise and repeated episodes of haematuria. Several urine cytological studies were negative for neoplastic cells. Imaging studies led to the patient's surgical intervention, which revealed an atrophic left kidney and a large 'tumour mass' encompassing the theoretical exit of the left internal iliac artery, left ureter, pouch of Douglas, rectum and lateral peritoneal surface. Due to the technical difficulties involved in enucleating such a lesion, a ureteral sample was taken and submitted for histopathological diagnosis with the suspicion of ureteral carcinoma. The macroscopic study of the referred material showed an irregular whitish tissue with an elastic-firm consistency and fibrous appearance, which on serial sections showed a fine reddish stippling that was difficult to appreciate. Histological examination revealed a ureteral segment with multiple intramuscular dilated glandular structures lined by endometrial epithelium whose immunohistochemical staining was strongly positive for cytokeratins, oestrogen receptors and progesterone receptors. Enveloping the ureteral wall was abundant disordered fibrous tissue with signs of haemorrhage. With all these data, the diagnosis of intrinsic ureteral endometriosis was made, although the intense extra-ureteral tissue response and the clear signs of haemorrhage that accompanied it led us to think of an accompanying extrinsic component, although no glandular structures were identified at that level.