PURPOSE: To assess wheter there would be a discrepancy in perineal sonography performed in the supine and standing position in the evaluation of stress urinary incontinence. MATERIALS & METHODS: Ultrasonography was performed to 42 female patients with stress urinary incontinence. Sagittal images through the bladder, urethrovesical junction and urethra were obtained from the perineal area. The posteriorurethrovesical angle (PUVA) and the distance of bladder neck descent were measured at rest and during Valsalva's maneuver in both supine and standing postion.. The difference of the values obtained in the supine and standing position was statistically evaluated by paired t-test. The number of positive results was also compared between the two positions. RESULTS: In the supine position, mean value of PUVA was 121.8 +/- 18.5(standard deviation) at rest, 145.5 degrees +/- 27.7 during Valsalva's maneuver, and the difference was 23.7 degrees +/- 24.4. The eistance of bladder neck descent was 10.7mm degrees +/- 6.0. In the standing position, mean PUVA was 132.9 degrees +/- 19.3 at rest, 159.7 degrees +/- 29.2 during Valsalva's maneuver, and the difference (deltaPUVA) was 26.8 degrees +/- 21.2. The distance of bladder neck descent was 10.4mm degrees +/- 6.1. Both values of the PUVA obtained at rest and during Valsalva's maneuver in the standing position were higher than the value obtained in the supine position(p<0.001, respectively), but the deltaPUVA was not significantly different between in the supine and in the standing position(p>0.1). However, the numbers of cases showing positive results were increased from 27 cases on supine position to 37 cases on standing position. CONCLUSION: PUVA and deltaPUVA can be significantly different on changing position, but BND is not affeted by changing position. Examination in the standing position can increases the positive result of the diagnosis of SUI.