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. Editorial Comment: The authors address an important but infrequently discussed topic. As Humpty Dumpty said, “When I use a word, it means just what I choose it to mean— neither more nor less.” 1 Alice replied, “The question is whether you can make words mean so many different things.” Humpty Dumpty responded, “The question is which is to be master—that’s all.” The International Continence Society definition of MUI is “the complaint of involuntary leakage associated with urgency and also with exertion, effort, sneezing or coughing.” The authors conclude, “Until a standard operational definition is available, we recommend that researchers characterize subjects with MUI using distinct descriptions of both urge and stress subcomponents.” This would indeed be helpful but we need to recognize that there is a very large group of patients who have “mixed symptoms” rather than MUI: those who have stress urinary incontinence and symptoms of overactive bladder (the definition requires that urgency be present) but without urgency urinary incontinence. Is this group simply a group that is less affected by their overactive bladder symptomatology and better able to suppress detrusor overactivity, or does it constitute a very distinct group with respect to characteristics and response to therapy?