The study was a clinical series of 95 ambulatory women with urinary incontinence. After voiding, each subject was scanned with a BladderScan BVI 2500, then catheterized for postvoid residual (PVR) and then scanned again. The mean PVR obtained by ultrasound was 49 ml, significantly larger than the mean PVR of 32 ml obtained by catheterization. Correlation analysis showed that the difference was not related to age, weight, body mass index, parity, pelvic prolapse or prior incontinence surgery, but was associated with prior hysterectomy and uterine prolapse. Regression analysis revealed that the difference was independently related to prior hysterectomy only. Postcatheterization ultrasound detected a mean of 22 ml, suggesting that the difference between the PVR values may be due to residual urine not removed by catheterization. Finally, ultrasound had a sensitivity of 66.7% and a specificity of 96.5% in detecting PVR ≥ 100 ml. Portable ultrasound scanners are quick, easy to use, reasonably sensitive, and very specific for determining elevated PVR.