PURPOSE: We identified predictors of passing a voiding trial after incontinence surgery with a mid urethral sling and examined if successful performance on a voiding trial was maintained. MATERIALS AND METHODS: A total of 89 women scheduled for incontinence surgery were enrolled from July 2005 until April 2006. Voiding trials were performed the day of discharge from the hospital, with a two-thirds volume void after a 300 ml fill considered passing. Those who passed underwent a second voiding trial 3 hours later. RESULTS: Of the participants 60 (67.4%) underwent tension-free vaginal tape surgery, 29 underwent transobturator tape (32.6%) and 64 (71.9%) underwent concurrent vaginal repairs. A total of 59 (67.0%) participants passed the first voiding trial. Univariate analysis identified 12 potential predicting variables for passing the first voiding trial. From these 12, model building via backward stepwise logistic regression found maximum flow on preoperative uroflowmetry to be the only significant predictive variable (p = 0.0002). Of the 59 women who passed the initial voiding trial 9 (16.4%) failed the second voiding trial. None of the 11 participants who had maximal flow rates greater than 30 cc per second failed the first or second voiding trial, whereas 17 of 22 subjects (77.3%) who had maximal flow rates less than 15 cc per second failed either of these trials. CONCLUSIONS: Maximum flow rates on preoperative uroflowmetry were the best predictor of passing an initial voiding trial after undergoing a mid urethral sling procedure for incontinence. However, the ability to maintain performance on a second voiding trial, even only 3 hours after passing an initial trial, is not assured.