PURPOSE: To evaluate the usefulness of endoanal ultrasonography and to determine the imaging features of patients with fecal incontinence, anal abscess or anal fistula. MATERIALS AND METHODS: Twenty five patients underwent endoanal ultrasonography between October 1995 and July 1996. Ten of these were fecal incontinence cases, eight had an anal abscess, and seven, an anal fistula. The incontinence grading scale (IGS) was used for clinical grading of fecal incontinence and pudendal nerve terminal motor latency (PNTML) for pudendal nerve injury. Endoanal ultrasonographic features and operative findings were retrospectively reviewed. RESULTS: Endoanal ultrasonography revealed defective sphincteric muscles in all three patients with myogenic fecal incontinence, but in six of seven cases with neurogenic fecal incontinence, these muscles were not defective. Myogenic and neurogenic incontience showed different findings (p=0.033). In comparison with surgical findings, endoanal ultrasonography was 88% accurate in anal abscess cases and 86% accurate in those of anal fistula. CONCLUSION: Endoanal ultrasonography in conjunction with PNTML was very useful for the detection of the site and severity of sphincteric muscle defect and diagnosis of the etiology of fecal incontinence. Through analysis of the site and type of lesion, the procedure can also serve as a guide to the surgical treatment of patients with anal abscess or fistula.