A 47-year-old woman was admitted when a mass in the urinary bladder was pointed out on ultrasound follow-up after hysterectomy for uterine myoma. Cystoscopy, ultrasonography, CT scan and MRI suggested a tumor in the muscle layers of the urinary bladder. Since the possibility of malignancy could not be ruled out, partial cystectomy was performed. The tumor was diagnosed as endosalpingiosis, a subclassification of mullerianosis histologically. The concept of endosalpingiosis has appeared recently and only 3 cases have been reported none of who had severe symptoms. Our case is the forth in the world. One of these cases had been treated with hormonal therapy as endometriosis, with no effect. Therefore, surgery is recommended as the first treatment of choice.