 Pelvic organ prolapse is a common and distressing condition that is frequently associated with stress urinary incontinence SUI and often requires surgical repair. Abdominal sacral colpopexy is the preferred operation for repairing pelvic prolapse. As many as 91 of women with pelvic organ prolapse undergoing sacral colpopexy also experience SUI. In addition, up to 44 of previously continent women develop SUI incontinence after sacral colpopexy: perhaps because a sacral colpopexy may predispose to opening of the bladder neck if secured too tightly. The selection of a surgical procedure to prevent and manage SUI in women undergoing sacral colpopexy is empiric rather than evidence-based. Conceptually, a mid-urethral sling may be more effective than a Burch procedure for preventing urinary leakage because a sling provides outlet resistance beyond the bladder neck and therefore it may compensate for a downward tension on the bladder neck resulting from the sacral colpopexy. Indeed, clinical observations suggest that a mid-urethral sling is effective among women who have persistent urinary incontinence after sacral colpopexy with a Burch procedure. Therefore, the investigators global hypothesis is that a mid-urethral sling is preferable to a Burch procedure for preventing and improving stress urinary incontinence in women undergoing sacral colpopexy for pelvic organ prolapse. The investigators SPECIFIC AIMS are to evaluate objective and subjective outcomes at 6, 12 and 24 months in 124 women with urinary incontinence and advanced pelvic organ prolapse. All women will be undergoing a sacral colpopexy and will be randomized to either a Burch procedure or a mid-urethral sling. The primary endpoint is composite continence at 6 months while secondary endpoints will include composite continence and subjective measures of incontinence, patient satisfaction and morbidity associated with these procedures. The investigators hypotheses are as follows: 