Background and purpose: Urodynamic studies (UDS) are routinely obtained prior to surgery for stress urinary incontinence (SUI) despite a lack of evidence that UDS information has an actual impact on outcome. The primary aim of this non-inferiority randomized clinical trial is to determine whether women with symptomatic, uncomplicated SUI who undergo only a basic office evaluation (BOE) prior to SUI surgery (No UDS arm) have non-inferior treatment outcomes compared to women who have BOE and UDS (UDS arm). Secondary aims are: 1) to determine how often physicians use preoperative UDS results to alter clinical and surgical decision-making, 2)to compare the amount of improvement in incontinence outcomes, and 3) to determine the incremental cost and utility of performing UDS compared with not performing UDS. Methods: After an initial basic office evaluation, women planning surgery for uncomplicated SUI who consent to study participation will be randomized to receive preoperative UDS or No UDS. Treatment will be planned and performed by the surgeon utilizing all the data available to them. We will compare results from the basic office evaluation (No UDS) with results from the basic office evaluation and preoperative UDS. Results: The primary outcome will be measured at 12 months using responses to the Urogenital Distress Inventory and the Patient Global Index-Improvement. Conclusions: Randomized trials comparing the effects of different diagnostic alternatives on treatment outcomes pose study design challenges. A non-inferiority design is appropriate when comparing a less invasive and less expensive alternative with a standard of care approach. © 2009 Elsevier Inc.