In 40 gynecological patients 44 different determinations of the bladder volume were made using ultrasonic methods. The product of bladder depth, height, and width, as determined from transverse and sagittal scans, showed the best correlation with the bladder volume measured by urethral catheter (r = 0.981). For 73% of the measurements the error was under 20% when the true bladder volume was > 100 cm3. This method gives a reasonable assessment of the bladder residual volume. It is quick, safe, and repeatable and, therefore, useful in postoperative clinical practice.