PURPOSE:This study was designed to review a 20‐year experience of the treatment of patients with anal fissure to identify possible etiologic factors and to explore effective preventative measures and the ideal treatment for this disease.METHODS:From January 1972 to December 1991, 1,391 patients (700 males, 691 females; average age, 39 years) with chronic symptomatic anal fissures underwent surgical treatment using either open or closed techniques. The following procedures were performed: 1) internal sphincterotomy for 1,313 idiopathic fissures; 2) C‐anoplasty for 36 cases of anal stricture; 3) debridement and sphincterotomy for 25 patients with postsurgical nonhealing wounds; 4) bilateral excision of the protruding internal sphincter for 17 patients with “subluxation.” Acute superficial anal fissures were treated conservatively, with emphasis on anal hygiene.RESULTS:Acute superficial anal fissures responded well to conservative management. Over 95 percent of patients with chronic anal fissures treated by surgery had satisfactory relief of symptoms. Early complications included urinary retention (1.4 percent), bleeding (1.1 percent), and abscess and fistula formation (0.7 percent). Late complications manifested as flatus and liquid incontinence (1.5 percent), delayed wound healing (1.4 percent), recurrence of fissures (1.3 percent), and symptomatic itching and burning (1.1 percent). The complication rate was higher in the group that underwent closed sphincterotomy than in the group treated by open techniques.CONCLUSIONS:Proper anal hygiene is important in both prevention and initial conservative management of symptomatic anal fissures. For chronic intractable cases, open lateral internal sphincterotomy is strongly recommended. C‐anoplasty should be done when strictures are present. Excision of the protruding internal sphincter is recommended in patients who present with an excessively elongated, tight anal canal with a partially protruding internal sphincter.