Objective: To validate transperineal ultrasound (US) in the assessment of urethrovesical junction hypermobility. Methods: In this prospective study carried out between 1999 and 2003 at a university medical centre we enrolled 100 women with genuine stress urinary incontinence (study group) and 50 continent women (control group). All women underwent the diagnostic protocol including urodynamic measurement and transperineal US scan using an abdominal semicircular 3.5 MHz linear array transducer. The position of the urethrovesical junction was described in relation to the inferior edge of the symphysis pubis by two parameters: the cephalocaudal and the ventrodorsal distance. The position and degree of urethrovesical junction descent during stress (3 consecutive coughs) were meas-ured and the results compared between the groups. Classification performance was evaluated by sensitivity and specificity. Results: There was no significant difference in the horizontal plane of the urethrovesical junction at rest and in the backward displacement duringstress between the groups. The downward displacement of the urethrovesical junction showed an average descent of 16.10 ± 4.01 mm in the study group vs. 7.92 ± 2.85 mm in the control group; the difference between the groups was statisticlly significant (p = 0.001) Considering the 12 mm cut-off value of the descent, US evaluation had an 88% specificity, and a 92% sensitivity, the PPV and NPV were 96 % and 79 %, respectively. Conclusions: We found a significantly greater downward displacement of the urethrovesical junction during stress in women with stress urinary incontinence compared to healthy controls. We may conclude that trasperineal US canaccurately visualise a hypermobile urethrovesical junction.