The Maximum Urethral Closure Pressure (MUCP) and Functional Urethral Length (FUL) are significant parameters of the Urethral Pressure Profile (UPP), while the Q-tip angle and Bladder Neck Descent (BND) are the significant parameters of urethral hypermobility. We performed a study to evaluate the effects and predictive values of each of these parameters in the diagnosis of Stress Urinary Incontinence (SUI). A retrospective study was done involving 90 SUI patients and 38 non-SUI patients who underwent urodynamic study, Q-tip test and perineal ultrasound at Yonsei Medical Center between January, 1999 and February, 2002. There was no statistical difference between the SUI and non-SUI groups in terms of mean age, delivery history, menopausal age and body mass index. While the FUL and Q-tip angle showed significant differences (33.18 ± 19.55 vs 33.12 ± 13.37 mm, p=0.002; 65.94 ± 21.69 vs 56.45 ± 26.53°, p=0.02, respectively) neither the MUCP nor the BND showed any significant difference between the two groups (60.06 ± 29.92 vs 48.97 ± 42.95 cmH₂O, p > 0.05; 1.09 ± 0.75 vs 0.85 ± 0.76 cm, p > 0.05; 0.71 ± 0.80 vs 0.53 ± 0.72 cm, p > 0.05). The odds ratios for the FUL and Q-tip angle were 1.038 (1.014, 1.061) and 1.017 (1.001, 1.033), respectively. The FUL and Q-tip angle had cut-off values of 1.36 cm (sensitivity: 68.8%, specificity : 54.1%, PPV : 73.8%, NPV : 48.1%) and 20.47° (sensitivity : 93.3%, specificity : 18.17%, PPV : 68.2%, NPV : 60%), respectively, in the diagnosis of SUI. The area under the curve (AUC) of the FUL and Q-tip angle were on average 0.625 (p=0.0016) and 0.575 (p=0.0012), respectively. Both the FUL and Q-tip angle showed a significant difference between SUI patients and the normal group. However, their value as a diagnostic tool was trivial, and since their sensitivity, specificity, positive predictive value and negative predictive value showed inconsistent results at each cut-off value, it would be difficult to apply them to clinical use. A further study is required to set-up standard diagnostic values of these variables for clinical use.