This study introduced the Kalman filter procedure for tracking urinary bladder filling from intermittent bladder volume measurements taken by an ultrasonic bladder volume monitor. The Kalman filter was based on a double integrator as a model for the bladder filling process between micturitions and included a procedure to reset the filter in the event of a micturition. The performance of the Kalman filter was evaluated experimentally using an ultrasonic bladder volume monitor on seven male urologic patients. During cystometry, saline was infused into the patient's bladder at a constant rate of 30 ml min(-1) until it was full, and the volume of the bladder was recorded every 30 s by the bladder volume monitor. The evaluation showed that the filter significantly improved the precision of the measured volumes in terms of mean absolute errorby 4.2 ml (95% confidence interval: 0.7-7.7 ml) (p = 0.025) without affecting the system accuracy, i.e. slope (p= 0.92) and intercept (p= 0.32). Finally, the micturition reset procedure was verified using simulated data.