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Introduction: Anal ultrasound, using a rigid, non-endoscopic trans-rectal ultrasound probe, is reported to accurately diagnose anal sphincter defects due to post-obstetrical trauma in the evaluation of fecal incontinence. However most gastroenterologists in the United States who perform EUS use a radial scanning echoendoscope system designed with fiberoptic or video optics to assist in upper GI endosonography, and not a dedicated rigid rectal ultrasound probe system. The purpose of this study was to evaluate the utility of a flexible UGI echoendoscope for diagnosing anal sphincter defects. Methods: Female patients referred for anal sphincter EUS to evaluate fecal incontinence from 11/95-10/99 were included in this retrospective analysis. Anal EUS was performed with either the Olympus GF-UM20 or UM130 radial scanning flexible echoendoscopes. The probe tip was inserted blindly into the anal canal and imaging was performed at 7.5 and 12 MHz without filling the balloon with water. The anterior aspects of the internal (IAS) and external (EAS) anal sphincters were examined for hypoechoic defects, which were reported as percent of circumference. IAS thickness was measured from the posterior aspect. Results: 49 women underwent EUS examinations. The median age was 53 (range 27-61). 38 (78%) had some form of defect detected, with 16 (33%) having both IAS and EAS defects, 20 (41%) isolated EAS defect, 2 (4%) isolated IAS defect, and 11 (22%) no defects. Patients with anterior IAS defects had a median defect of 37% (15-50%). Patients with anterior EAS defects had a median defect of 35% (10-60%). The IAS thickness was a median of 3 mm (1-4 mm). Among the 12 patients who also underwent anal manometry, 9/12 patients had both normal IAS and normal resting anal sphincter pressures. All 12 patients had low anal sphincter squeeze pressures, and 7/12 also had EAS defects. During median follow-up of 12.5 months (2-48), 10/36 (28%) patients with EAS defects underwent surgical sphincteroplasty. Conclusions: 1. EUS using a flexible upper GI echoendoscope can diagnose post-obstetrical anal sphincter defects. 2. Anal EUS information complements anorectal manometry. 3. Most patients with EUS anal sphincter defects do not undergo surgical sphincteroplasty. 4. Anal sphincter EUS performed with a flexible UGI radial scanning echoendoscope can be used in the evaluation of fecal incontinence if rigid anal ultrasound probe equipment is not available. This work was supported in part by a grant from the ASGE/ADHF.