The usefulness of biplanar endosonography of the anal canal was evaluated. Twenty women with fecal incontinence underwent endosonography of the anal canal. All examinations were performed using both sector and sagittal endorectal probes. Images were obtained in the axial and sagittal planes. Isolated external anal sphincter tears were missed on axial images in 3 out of 10 cases. In all 10 cases, the sagittal scans confirmed external anal sphincter defects. Routine scanning of the anal canal in the axial and sagittal planes increases the detection rate of external anal sphincter defects on endosonography.