BACKGROUND: The levator ani muscle (LAM) plays an important role in urinary continence, but the anatomical relationship between this pelvic floor muscle and the external urethral sphincter (EUS) remains incompletely understood. OBJECTIVE: To investigate the topographical relationship between the EUS and the LAM. DESIGN, SETTING, AND PARTICIPANTS: Serially sectioned and histochemically stained foetal pelves from eleven females and nine males (10-27 wk of gestation) were studied. Three foetal pelves (two female, 12 and 18 wk of gestation; one male, 12 wk of gestation) and three adult pelves (two females, 54 and 85 yr; one male, 75 yr) were stained immunohistochemically for the presence of striated and smooth muscle tissue. Three-dimensional reconstructions were prepared. MEASUREMENTS: Anatomy of the LAM and urethral sphincter components was evaluated qualitatively. RESULTS AND LIMITATIONS: The EUS has no direct bony attachment. In female foetuses, the inferior part of the EUS is firmly attached to the LAM by a tendinous connection. Contraction of this part of the EUS produces a force on the urethra in a posteroinferior direction. Contraction of the LAM compresses the rectum and moves the rectovaginal complex anteriorly and superiorly towards the urethra in a plane that lies parallel to, but superior of, that of the EUS. Simultaneous contraction of the LAM and EUS causes an anteriorly convex bend in the midurethra, which closes the midurethral lumen. A similar attachment of the EUS to the LAM is absent in the male. Our study is limited due to the absence of young adult study specimens. CONCLUSIONS: The EUS in females is anchored to the levator ani muscle via a tendinous connection. Because of this attachment to the LAM, proper function of the EUS is dependent on the integrity of the LAM and its attachment to the pelvic wall.