Twenty-four women with primary suture of an obstetric tear of the anal sphincter were examined with anal endosonography a median of 12 (range 3-18) months after delivery. Endosonography was normal in ten patients, of whom one was incontinent. The examination showed a defect in the external anal sphincter in 13 patients; six of these were incontinent, two of whom had normal findings on palpation. An isolated internal sphincter defect was found in a continent patient. Since anal endosonography causes no more discomfort than digital examination, it may be useful to identify patients who would benefit from surgical reconstruction of the anal sphincter.