Six hundred and forty patients (65 of them were children) with acute and chronic anal fissure were randomized to receive topical 0.2%-0.8% Glyceryl trinitrate (G.T.N.) or Isosorbide dinitrate (ISDN) 1%-3% three times daily digitally applied ointment. Patients were followed for 6-26 months. A course of 2-6 weeks treatment was needed. Resting and maximum anal sphincter pressure (MARP) were measured by manometry for 40 patients and showed a very significant decrease in maximum anal sphincter pressure after application of ointment with progress of days of treatment (p =0.02). After 1-2 weeks of treatment 90.4% of acute fissure patients were free of symptoms and 83.73% of them were later cured. Four to eight weeks of treatment were needed to abolish pain in 85.5% chronic fissure patients, and cure was clear in 80% of them (p = 0.008). Side effects of treatment were negligible. Recurrence rate was 4%, while 24 patients (3.8%) were sent for internal sphincterotomy and 81 patients (12.6%) requested revision of medical treatment. In this study we concluded that surgery can be avoided in most cases of anal fissure, and it kept for recurrent cases. Recurrent cases after surgery can also be treated medically