INTRODUCTION AND HYPOTHESIS: Midurethral sling (MUS) is now the first line surgical treatment for female stress urinary incontinence. Our aim was to identify predictors for MUS failure. METHODS: A total of 1,225 consecutive women with urodynamic urinary stress incontinence had a synthetic MUS (955 retropubic and 270 transobturator) at our institution between 1999 and 2007. Multivariate analysis was performed in order to identify independent risk factors for failure. RESULTS AND CONCLUSIONS: At a mean follow-up of 50 +/- 24 months (range, 12-114), the subjective cure rate was 84.7 . Multivariate analysis revealed that BMI >25 (OR, 2.9), mixed incontinence (OR, 2.4), previous continence surgery (OR, 2.2), intrinsic sphincter deficiency (OR, 1.9), and diabetes mellitus (OR, 1.8) are significant independent predictors for MUS failure. Concomitant prolapse surgery decreased the likelihood of surgical failure after MUS (OR, 0.6). Patient s age and the type of the sling were not found to be risk factors for surgical failure.