Purpose We aimed to explore operational definitions of mixed urinary incontinence (MUI) for use in incontinence outcomes research for non-surgical patient populations. Methods A secondary analysis of women with urge incontinence or urge predominant MUI enrolled in the Urinary Incontinence Treatment Network BE-DRI randomized clinical trial was performed. Subjects were characterized at baseline for urinary incontinence severity and incontinence subtype (stress or urge) using the Medical, Epidemiologic, and Social Aspects of Aging (MESA) questionnaire, the Urogenital Distress Inventory, and a 7-day urinary diary. Various different definitions of MUI, ranging from low to high threshold, were created using a combination of these baseline incontinence measures. Prevalence of MUI based on each definition was described and compared to treatment response. Logistic regression analysis was used to estimate the association between the study outcomes and the different definitions of MUI. Results The 307 participants in the BE-DRI study had a mean age of 56.9 (±13.9) years with a mean total MESA score of 21.7 (±8.9) and a mean total UDI score of 120.5 (±49.6). The proportion of women diagnosed with MUI varied significantly by definition ranging from 63.5% to 96.4%. Low threshold symptom-based definitions resulted in nearly universal diagnosis of MUI. No strict cut-off value for these baseline measures was identified to predict clinical outcomes. Conclusions Current MUI definitions do not adequately categorize clinically relevant UI subgroups. For research purposes we believe it necessary to describe the severity of each incontinence subtype separately in subjects with MUI. Neurourol. Urodyn. 30:47-51, 2011. © 2010 Wiley-Liss, Inc.