Endometriosis occurs when a tissue resembling endometrial glands and stroma grows in ectopic sites, commonly causing infertility and pain. This condition is most often seen in women of reproductive age, involving pelvic sites such as the ovaries, broad ligaments, uterosacral ligaments, and posterior cul-de-sac. Very rarely, endometriosis has also been found in the lower genitourinary tract of men. A 40-year-old man presented to his primary care physician with abdominal pain. Further imaging discovered a midline mass. Surgical removal of the mass and histological investigations led to the diagnosis of endometriosis. There are multiple theories on the etiology of both female and male endometriosis. The prevailing risk factor proposed in previous cases of male endometriosis is prolonged exposure to estrogen therapy. Should endometriosis become symptomatic, cessation of estrogen therapy and careful surgical intervention may successfully relieve the associated symptoms.