In order to increase our knowledge of the physiopathology of urinary stress incontinence related to pelvic relaxation, the Authors examined 20 women suffering from SUI (Stress Urinary Incontinence) almost always characterized by concomitant slight or moderate urethrocystocele and 20 women without urological problems. They analyzed and compared the measurement of perineal descent with radiological and electromyographic parameters in order to detect if a suffering of some fibers of the pudendal plexus can be related to the pathology of SUI. They pointed out that patients affected by SUI show a perineal position, either at rest and under switch, below the ischial tuberosities plane. Furthermore the anterior angle at rest is always more than 30 degrees and electromyographic records are pathological in 90% of cases.