Müllerianosis of the urinary bladder is a rare condition that encompasses 3 histological entities (endometriosis, endocervicosis, and endosalpingiosis). The authors report 2 patients with bladder müllerianosis, one of whom had endometriosis and the other a history of past pelvic surgery, describe the histological and cystoscopic features, and review the literature on this condition. Mucosal hyperemia and submucosal nodules or cysts with associated fibrosis and distortion of the bladder wall may mimic malignancy on cystoscopy, as may the infiltrative growth pattern sometimes evident histologically. Recognition of this complex diagnostic entity is important to avoid misdiagnosis and inappropriate investigation. There is a clinical association with endometriosis and past pelvic surgery.