We developed a new, affordable, and easy-to-use natural-fill cystometric device to overcome the limitation of conventional cystometry, long been criticized for being unphysiological. The device was composed of one transurethral catheter, one rectal catheter, two digital manometers, and a portable computer. The transurethral and rectal catheters were connected to manometers, which were then connected to the computer. Three persons with neurogenic bladder were recruited for testing the device. To shorten the test duration, we gave patients 500 ml water before the test. As urine filled inside the bladder, the transurethral and rectal catheters transmitted respectively the intravesical and abdominal pressures to the digital manometers. The pressures were stored within the portable computer and turned into graphs indicating pressure changes. The natural-fill cystometry is thought to be a physiological test that is affordable and convenient because of its simple structure and small size. (J Korean Acad Rehab Med 2006; 30: 195-198)