Chronic anal fissures are usually treated by internal lateral sphincterotomy. Nitric oxide donors like glyceryltrinitrate (GTN) have shown their efficacy in a series of patients with anal fissure treated by the means of the so-called reversible chemical sphincterotomy. The present study deals with a prospective, randomized, clinical trial on thirty patients to test whether the topical application of 0.2% GTN Ointment is an effective medical treatment in comparison to surgical sphincterotomy. MRAP (Maximum Resting Anal Pressure) was measured before and after each procedure.