PURPOSE: The modified Hanley technique, which is used for treatment of a deep horseshoe fistula, has reduced damage to the external anal sphincter compared to the classic Hanley technique, but its shortcoming is that it causes inconvenience to the patient due to the fact that a drainage tube must be left in place for a long time. To solve this problem, the authors devised a self-pulsed washable seton and then compared the results of its use to determine its clinical usefulness. METHODS: The subjects of this study were 34 patients who were diagnosed with a deep posterior complex anal fistula and who were operated on by using the modified Hanley technique between January 1999 and December 2004. Twelve patients who were treated with the self-pulsed washable seton were classified as Group A, and 12 patients who were treated by using a conventional loose seton were placed in Group B. These two groups were compared for period of purulent discharge, period of leaving the seton alone, and recurrence rate. RESULTS: The period of purulent discharge was 18.75 days (15~24) for group Aand 29.75 days (24~37) for group B. The period of leaving the seton was 21.58 days (18~29) for group A and 32.58 days (28~39) for group B. The recurrence rate after surgery was 8.3% in group A and 16.7% in group B. CONCLUSIONS: The self-pulsed washable seton devised by the authors shortened the treatment period through more effective wound management, so we propose using it as a new method for treating a deep posterior horseshoe fistula.