A 41-year-old female patient presented with left-sided flank pain and gross hematuria temporally unrelated to her menstrual cycle. Abdominal computed tomography scan showed a large left-sided solid, enhancing kidney mass radiographically consistent with renal cell carcinoma. Following surgical resection, histopathological examination revealed polypoid endometriosis. Polypoid endometriosis is rare and mimics a neoplasm clinically, radiographically, and on gross examination. Patients with polypoid endometriosis often present with symptoms related to mass effect rather than classic endometriosis hallmark symptoms such as dyspareunia, dysmenorrhea, and cyclic abdominal pain. Treatment includes surgical resection.