OBJECTIVE: To evaluate characteristics associated with treatment failure 1 year after midurethral sling in women with mixed urinary incontinence. METHODS: Four hundred three women who participated in a randomized trial that compared midurethral sling and behavioral and pelvic floor muscle therapy (combined group) against midurethral sling alone for mixed incontinence with 1 year of follow-up data were eligible for this planned secondary analysis. Overall treatment failure was defined as meeting criteria for subjective failure, objective failure, or both. Subjective failure was defined as not meeting the minimal clinically important difference for improvement on the UDI (Urogenital Distress Inventory)-total score (26.1 points). Objective failure was not achieving 70% improvement on mean incontinence episodes of any type per day or having undergone any additional treatment for urinary symptoms at 12 months postoperative. Logistic regression models for treatment failure were constructed. Independent variables included site and treatment group, and clinical and demographic variables based on bivariate comparisons (P<.2). Treatment group interaction effects were evaluated. RESULTS: Previous overactive bladder medication use (unadjusted odds ratio [OR] 2.19, adjusted odds ratio [aOR] 1.89, 95% CI 1.10-3.25), detrusor overactivity on cystometrogram (OR 2.25, aOR 2.72, 95% CI 1.53-4.84), body mass index (OR 1.29, aOR 1.27, 95% CI 1.03-1.57), and Valsalva leak point pressure less than 60 cm H2O (OR 1.96, aOR 3.13, 95% CI 1.65-5.94) were associated with overall failure. Worse UDI urgency scores were associated with failure in the midurethral sling-alone group. Sling type (retropubic vs transobturator) was not associated with failure. CONCLUSION: Certain clinical and urodynamic variables are associated with treatment failure after midurethral sling among women with mixed urinary incontinence. Women with more severe urgency symptoms at baseline may benefit from perioperative behavioral and pelvic floor muscle therapy combined with midurethral sling. This information is helpful for counseling women with mixed incontinence who are considering surgery. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT01959347.