Recent developments of ultrasound imaging have contributed much to the understanding of urodynamics in patients with lower urinary tract symptoms (LUTS). These include ultrasound estimated bladder weight (UEBW), transrectal power Doppler imaging of the prostate and transrectal ultrasonography during voiding (voiding TRUS). UEBW, which is obtained by measuring the thickness of the anterior bladder wall using a 7.5 MHz probe, represents well the degree of bladder hypertrophy caused by obstruction. This parameter is, accordingly, of clinical use in the evaluation of obstruction. The UEBW predicted the presence of obstruction as determined by pressure-flow study with a diagnostic accuracy of 73%. Transrectal power Doppler imaging of the prostate has made it easy to detect prostatic vessels and furthermore to obtain their resistive index (RI). Accumulating data suggest strongly that RI reflects the intraprostatic pressure. More interestingly, RI decreases significantly during voiding in normal subjects but not in patients with benign prostatic hyperplasia. Thus, this method is of particular use in monitoring noninvasively the dynamic change in intraprostatic pressure during voiding. Voiding TRUS makes it possible to monitor the movement of not only the posterior urethra but also the prostate during voiding. Based on our recent study, the anterior fibromuscular stroma (AFMS) seems to contract to open the urethra. Although the physiological function of the AFMS in the prostate remains unknown, AFMS may play a significant role in normal micturition. Due to its noninvasiveness and ease of application, ultrasound imaging would play a vital role in the diagnostic process for patients with LUTS in future.