Endometriosis is a common gynecologic disorder characterized by ectopic endometrial tissue growth outside the uterine cavity. Although usually occurring in pelvic organs, endometrial lesions may involve urinary tract. Renal endometriosis is extremely rare and it has only occasionally been reported in the past. We report two cases of patients with renal cystic lesions, incidentally found at imaging techniques during oncologic follow-up for gastric sarcoma and melanoma, initially misinterpreted as complicated haemorrhagic cysts and then histologically characterized as renal localizations of extragenital endometriosis.