AIMS: To determine if pre-operative urodynamic testing (UDS) affects physicians' diagnostic confidence and if physician confidence affects treatment outcomes at 1 year. METHODS: The Value of Urodynamic Evaluation (ValUE) trial randomized 630 women with predominant stress urinary incontinence (SUI) to office evaluation (OE) or OE plus UDS prior to surgery. After OE, physicians completed a checklist of five clinical diagnoses: SUI, overactive bladder (OAB) wet and dry, voiding dysfunction (VD), and intrinsic sphincter deficiency (ISD), and reported their confidence in each. Responses ranged from 1 to 5 with; 1 = "not very confident (<50%)" to 5 = "extremely confident (95 + %)." After UDS, investigators again rated their confidence in these five clinical diagnoses. Logistic regression analysis correlated physician confidence in diagnosis with treatment success. RESULTS: Of 315 women who received OE plus UDS, 294 had complete data. Confidence improved after UDS in patients with baseline SUI (4.52-4.63, P < 0.005), OAB-wet (3.55-3.75, P < 0.001), OAB-dry (3.55-3.68 P < 0.005), VD (3.81-3.95, P < 0.005), and suspected ISD (3.63-3.92, P < 0.001). Increased confidence after UDS was not associated with higher odds of treatment success although mean changes in confidence were slightly higher for those who achieved treatment success. Physician diagnoses shifted more from not confident to confident for ISD and OAB-wet after UDS (McNemar's P-value <0.001 for both). CONCLUSIONS: In women undergoing UDS for predominant SUI, UDS increased physicians' confidence in their clinical diagnoses; however, this did not correlate with treatment success.