Stress urinary incontinence (SUI) was studied in 125 women who were subjected to simultaneous urodynamic and radiologic evaluation. This included cystometry, urethral pressure profiles, measurement of effective urethral length, estimation of urethral mobility, and alterations in the urethrovesical angles during stress. The most common abnormality was a hypermobility of the proximal urethra with loss of its intraabdominal position during stress, associated with changes in the urethrovesical angle. Fixation of the posterior urethra, loss of effective urethral length, low resting urethral pressure, and true neurovesical dysfunction were also found in some of the patients. Uninhibited bladder contractions were found in 22% of cases, but in most instances they were the result of SUI and ceased after surgical repair.