The outcome of aggressive surgical treatment of 64 symptomatic anal fistulas in 55 patients with Crohn's disease has been studied. Forty-one fistulas, in 33 patients, were treated by conventional fistulotomy (17 subcutaneous, 19 intersphincteric, 5 low transsphincteric fistulas). Thirty wounds (73 percent) healed within 3 months and eight more wounds (93 percent) healed within 6 months. Three wounds did not heal within 12-18 months. Two of these patients subsequently required proctocolectomy. Wound healing was not influenced by the presence of rectal Crohn's disease or granulomatous inflammation in the tract. No change in continence was experienced by 26 of the 33 patients who underwent fistulotomy. Three patients required proctocolectomy and the remaining four patients experienced minor degrees of incontinence postoperatively. Sixteen high transsphincteric, five suprasphincteric, and one extrasphincteric fistula in 22 patients were treated by laying open external tracts and placing a noncutting seton through the sphincter, which was left in place for prolonged periods to maintain drainage. During follow-up (6 months to 10 years, median 2.5 years), three fistulas healed and seven remained quiescent. Nine patients required further treatment by a new seton and three patients required proctocolectomy. Eight of the 22 patients who had a seton inserted had no change in continence, and six patients in this group developed minor changes in continence, mostly related to diarrhea associated with intestinal disease. Anal fistulas in Crohn's disease, which involve minimal sphincter muscle, can be successfully treated by fistulotomy. High fistulas should be treated with seton drainage to limit recurrent suppuration and preserve sphincter function.