Abstract: The aim of the present study was to determine the efficacy of topical sildenafil in the healing of chronic anal fissure. We conducted a prospective, randomized double blind controlled trial on 61 patients with symptomatic CAF lasting more than four weeks. After simple randomization, 31 and 30 patients were assigned to receive 0.75 mL of 10% sildenafil cream (t.i.d. intra-anal) and placebo for 7 days, respectively. Patients were advised to continue the medication for the next 2 days, if their symptoms were not resolved. All patients were followed up for 2-3 months after treatment. The primary end points of the study were complete healing of the CAF at least two months after the treatment or complications of the therapy. The rate of healing was significantly higher in Sildenafil group compared with controls (p<0.001). Of 31 patients in sildenafil group, 19 (61.2%) were improved after 7 days of treatment. The other 12 (38.8%) were also cured during the next 2 days of therapy. We did not detect any improvement during 9 days of treatment in patients enrolled as controls. After successful follow up of 28 patients in sildenafil group, 24 (86%) did not reveal any signs or symptoms of recurrence, while 4 (14%) patients experienced them during this period. The side effects were observed in two patients of sildenafil group which happened after complete course of treatment. Topical treatment by sildenafil was accompanied by 100 and 86% effectiveness in the short term and long term management of CAF, respectively. This treatment could be useful at least to reduce the number of CAF patients who needs surgical interventions.