OBJECTIVES: To investigate the accuracy of an ultrasound scanner for the measurement of bladder urine volume. MATERIALS AND METHODS: In a prospective study using a bladder scanner, 137 estimation of bladder volume were made in 129 male and 8 female patients. The instillation volumes of saline instilled into the collapsed urinary bladder via cystoscopy were compared with those estimated by a Bladder Scan ultrasound unit after saline instillation into the bladder. RESULTS: The mean volumes of saline instilled via cystoscopy and estimated by the BladderScan were 99.55±6.75 and 115.47±8.49 ml, respectively. The mean difference between the true instilled volume and the scanner estimation was 15.91 ml. The intraclass correlation showed a good correlation (rI=0.860, range 0.803-0.899). CONCLUSIONS: The results of this study suggest that this ultrasound scanner can serve as a useful tool to measure bladder urine voulume with satisfactory accuracy.