**Abstract**

A chronic anal fissure is one of the most encountered anorectal diseases in the clinical practice of general surgery. After all the medical therapies have failed, lateral internal sphincterotomy is still the main-stay treatment for chronic anal fissure. The optimal and standardized sphincterotomy has the utmost importance in preventing postoperative incontinence and recurrence, which are consequences of either extreme or insufficient sphincterotomy. Therefore, the lateral internal sphincterotomy technique has been evolved within years with the initial proposition of controlled-sphincterotomy and improvement of this technique with the addition of sphincterotomy up to the dentate line. This chapter focuses on the chronic anal fissure in the era of spasm-controlled lateral internal sphincterotomy.

**Keywords:** acute anal fissure, chronic anal fissure, internal sphincterotomy, spasm-controlled, incontinence
