OBJECTIVE Although anal endosonography provides clear images of anal sphincters, the probe in the anal canal may distort epithelial structures and sphincter muscles may be compressed, producing inaccurate muscle thickness measurements. The aim of this study is to describe a new approach using vaginal endosonography to image the anal canal undistorted. METHODS Twenty females (10 healthy volunteers and 10 with fecal incontinence) had both anal and vaginal endosonography performed. RESULTS The undisturbed anorectum, submucosa, anal cushions, and anal sphincter muscles were clearly visualized by vaginal endosonography, and anatomy was described. Although anal and vaginal endosonographic measurements of internal sphincter muscle thickness correlated (r = 0.83; P = 0.01), anal endosonography consistently underestimated the thickness (2.3 +/- 0.5 vs. 3.2 +/- 1.2 mm; mean +/- standard deviation). Anterior internal and external anal sphincter defects were identified accurately with both techniques. CONCLUSIONS Vaginal endosonography is a new technique that enables accurate imaging of anal sphincters and epithelial structures at rest. In addition to making the diagnosis of anal sphincter defects, it has potential applications in the imaging of anovaginal sepsis and malignancy and possibly in understanding the pathogenesis of anal fissure and hemorrhoids.