Forty patients who underwent a single tension-free vaginal tape procedure were evaluated by perineal ultrasound both pre- and postoperatively in a prospective observational clinical study. The positions of the tape, bladder neck and urethra were sonographically documented at rest and during Valsalva maneuvers. During Valsalva the tape rotated towards the symphysis in all patients. Postoperative urethral angulation could be demonstrated in 36 of 40 patients. Bladder neck mobility remained unchanged after the tension-free vaginal tape procedure, and 36 of the 40 were dry according to patient questionnaires. Postoperative cough test was negative in all patients. Two points seem to be important for the functioning of the tension-free vaginal tape: a dynamic kinking of the urethra during stress, and the movement of the tape against the symphysis, compressing the tissue between the tape and the symphysis. Mobility of the bladder neck is unaffected by the single tension-free vaginal tape procedure.