A portable ultrasound to determine bladder volume, the BladderScan 2500, was compared to transurethral catheterization in 72 women. Most measurements were made after voiding. Volumes measured by catheterization were 17 ml greater than those measured by ultrasound, which was not clinically significant. The BladderScan technique does not carry the risk of urinary tract infection or patient trauma, and patient dignity is preserved, while accurately determining urinary volume.