AIMS: To explore how baseline demographic, clinical, and urodynamic (UDS) variables correlate with measures of urethral function in women planning midurethral sling surgery. METHODS: Women with predominant stress urinary incontinence (SUI) as part of the trial of mid-urethral slings (TOMUS) were characterized preoperatively including: demographics, body mass index (BMI), responses to the Medical and Epidemiologic Social Aspects of Aging (MESA) and Urogenital Distress Inventory (UDI) questionnaires, pad weight (PW), incontinence duration, prior SUI surgery, prolapse, strength of pelvic contraction, Q-tip test, uroflow, cystometrogram, and detrusor pressures at maximum flow (Pdet at Qmax). Multivariate regression analysis and modeling confirmed variables with significant correlations with maximal urethral closure pressure (MUCP), functional urethral length (FUL), and Valsalva leak point pressure (VLPP). RESULTS: Five-hundred thirty-nine women were included in the analysis. In multivariable analyses, PW (P = 0.045) and age (P < 0.0001) were negatively correlated with MUCP (as PW and age increased, MUCP decreased); BMI (P = 0.02) and Pdet at Qmax (P < 0.0001) were positively correlated with MUCP (as BMI and Pdet at Qmax increased, MUCP increased). Age (P = 0.002) was negatively correlated with FUL; Qtip delta (P = 0.006), pelvic organ prolapse quantification examination (POPQ) stage (P = 0.002) and strength of pelvic contraction (P = 0.03) were positively correlated with FUL. Duration of incontinence (P = 0.01) was negatively correlated with VLPP; Qtip delta (P = 0.02), BMI (P = 0.0005) and Pdet at Qmax (P = 0.0005) were positively correlated with VLPP. CONCLUSIONS: Age, BMI, Qtip delta, and Pdet at Qmax were variables that correlated with two or more measures of urethral function. These correlations may help direct future research in female urethral function.