BACKGROUND : Chronic fissure in ano is the most common cause of pain during defecation in young patients. lateral anal sphincterotomy is the surgery of choice for chronic fissure in ano. This procedure can be done by either open or closed method. OBJECTIVE: The aim of this study was to compare the closed and open method LAS for chronic anal fissure . STUDY DESIGNS: The study was designed as a prospective randomized study. PLACE AND DURATION OF STUDY : The study was conducted in Indira Gandhi medical college and hospital , puducherry from January 2019 to november 2019. PATIENTS AND METHODS: A total of 205 patients undergoing surgery were divided into two groups. In group A, there were 100 patients who were treated by closed lateral internal anal sphincterotomy and in group B there were 105 patients who were managed by open lateral internal anal sphincterotomy method. Patients were followed up for 3 months following surgery to observe for pain, bleeding, infection, incontinence, and recurrence. RESULTS: There was significant difference in postoperative acute complications between the two methods of internal anal sphincterotomy. CONCLUSION: Lateral internal sphincterotomy either with open or closed method is the treatment of choice for chronic anal fissure. However, the closed method is considered to have less post operative complication compared to the open method.