Objective: To identify clinical and demographic factors predictive of midurethral sling failure. Methods: Overall treatment failure was defined by one or more of the following objective outcomes: a positive stress test, positive 24-hour pad test or retreatment for stress urinary incontinence (SUI); subjective outcomes: self reported SUI by the Medical, Epidemiologic and Social Aspect of Aging questionnaire, incontinent episodes by 3-day diary, or retreatment for SUI, or a combination of these. Logistic regression models adjusting for sling type and clinical site were used to predict odds of overall treatment failure after univariable analysis. Models were also fit to compare factors associated with objective failure and subjective failure only. Results: Previous UI surgery (odds ratio [OR] 1.99, 95% confidence interval [CI] 1.14-3.47); maximum Q-tip excursion<30° (OR 1.89, 95% CI 1.16-3.05); Medical, Epidemiologic and Social Aspect of Aging questionnaire urge score per 10 points (OR 1.97, 95% CI 1.21-3.21); and pad weight per 10 g (OR 1.06, 95% CI 1.02-1.10) were predictors of overall failure. Having concomitant surgery (OR 0.44, 95% CI 0.22-0.90) was predictive of subjective failure only rather than objective failure. Age per 10 years (OR 1.48, 95% CI 1.14-1.90); Urogenital Distress Inventory score per 10 points (OR 1.09, 95% CI 1.02-1.17); pad weight per 10 g (OR 1.05, 95% CI 1.01-1.10) were predictive of objective failure compared with subjective failure only. Associations of risk factors and failure were similar independent of sling type (retropubic or transobturator). Conclusion: Twelve months after surgery, risk factors for overall and objective treatment failure were similar in women undergoing retropubic and transobturator sling procedures. This information may assist in counseling patients regarding efficacy of sling procedures and in setting expectations for women at increased odds for treatment failure. © 2011 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.