Objective: To correlate structural intraurethral ultrasound findings with needle electromyography of striated urethral sphincters in young continent nulliparas.Methods: Twenty-three nulliparas, each less than 35 years old and without pelvic floor disorders, were recruited at Methodist Hospital in Indianapolis, Indiana, and the University of Louisville in Louisville, Kentucky. Each had concentric needle electromyography of their urethra to localize their striated urethral sphincter. Intraurethral ultrasound was used to identify the needle tip and layer in which it was found, examine the sonographic appearance of periurethral anatomy, and measure the thickness of hypoechoic and outer hyperechoic layers.Results: Three layers were seen on intraurethral ultrasound: a mildly hyperechoic inner layer, a hypoechoic middle layer, and a hyperechoic outer layer. The concentric needle tip was seen in all subjects and showed motor unit action potentials when located in the outer hyperechoic layer. The mean thickness of the hypoechoic layer was 2.5 mm, and the mean thickness of the outer hyperechoic layer was 2.6 mm.Conclusion: Motor unit action potentials showed that striated muscle was present in the outer hyperechoic layer on intraurethral ultrasound, implying that it contains the striated urethral sphincter. Copyright (C) 2000 The American College of Obstetricians and Gynecologists.