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INTRODUCTION AND OBJECTIVES: While mid-urethral sling (MUS) operation has expanded its application to more complicated cases such as the patients with mixed urinary incontinence (MUI), the success rates in the patients with MUI have been reported lower than the patients with pure stress urinary incontinence (SUI). If the failure of operation is predicted in the patients with MUI, one could change the therapeutic modalities to obtain the best results regarding continence and the risk factors for failure could help the physicians to counsel the patients ahead of operation. We evaluated and compared the risk factors for failure after MUS operation between pure SUI and MUI. METHODS: Two hundred and twenty-eight women were categorized into pure SUI (Group A, 163 patients) and MUI (Group B, 65 patients). Preoperative evaluations including symptom questionnaire, physical examination and urodynamic study were performed. Patients received the retropubic (17.5%) or trans-obturator (82.5%) MUS operations. RESULTS: Follow-up for Group A and B were 18.8 months (3-52) and 19.2 months (3-54), respectively. The demographic characteristics different between both group were body mass index, presence of cystocele, and severity of incontinence. The MUCP, VLPP, Q-tip and weight of 1-hour pad test were not significantly different in both groups. The success rate in Group A (95.7%) was higher than in Group B (84.6%) (p=0.015, Chi-Square test). In Group A, VLPP, PdetQmax and weight of 1-hour pad test were identified risk factors for failure of operation in univariate analysis, but, only weight of 1-hour pad test was independent risk factor in multivariate analysis (adjusted OR 3.5, 95% CI 1.204-8.895, p=0.045). In Group B, menopause without hormone replacement, AUA Symptom Index-QoL score, maximal cystometric capacity (MCC) and involuntary detrusor contraction (IDC) were the risk factors in univariate analysis, but MCC (adjusted OR 0.9, 95% CI 0.645-0.984, p=0.032) and IDC (adjusted OR 2.3, 95% CI 1.014-3.309, p=0.044) were independent risk factors in multivariate analysis. CONCLUSIONS: The risk factors for failure after MUS operation were different between pure SUI and MUI. Unlike pure SUI, weight of 1-hour pad test was not significant to predict the failure of operation in MUI. Meanwhile, MCC and IDC, indicating the pathophysiological status of the detrusor muscle itself, were important to predict the failure of operation in MUI.