Stress urinary incontinence (SUI) is a common problem in women. Successful treatment is now mid urethral sling but it would be a cause of urethral obstruction. In this case report, a 50 years old woman presented with a huge introitus mass after 3 months of midurethral sling. The mass protruded from the urethra and could not be reduced. Emergency MRI of pelvis was demonstrated prolapsed ureterocele, single system of right ureter. Preoperative planning was cystoscopy and mass excision. The patient was preoperatively counseled that right ureteric reimplantation may be required. Finally, the mass could be excised externally without reimplantation.