PURPOSE: This study was designed to assess differences between lateral internal anal sphincterotomy and anal advancement flap for chronic anal fissure. METHODS: Forty patients with chronic anal fissure were prospectively studied. Patients randomized to the sphincterotomy group (n = 20; median age, 34 (range, 16-61) years) underwent lateral internal anal sphincterotomy. Patients randomized to the flap group (n = 20; median age, 32 (range, 20-44) pears) had an anal advancement flap. RESULTS: All fissures in the sphincterotomy group healed following surgery compared with three patients that failed to heal in the flap group (P = 0.12). No patient in either group was incontinent to any degree following surgery. Patient satisfaction with surgery was similar in both groups. CONCLUSION: Anal advancement flap is an alternative to lateral sphincterotomy for chronic anal fissure.