INTRODUCTION: The anal fissure is a linear tear in the anal canal mucosa. If healing fails, it evolves into a chronic anal fissure (CAF). This is one of the most frequent proctologic problems affecting younger patients, altering their social and work life. As it is disabling disease, it causes a socioeconomic problem and, hence, it is important to make a proper diagnosis and apply a rapid and efficient treatment.At present, there are different therapeutic options, both medical and surgical. Among the first, there are several options that relax the anal sphincter. One of the options which are most used is the 0.2% Glycerol Trinitrate (GTN) ointment, there being some randomized and controlled studies reporting 48% and 69% healing rates and other studies with comparable results against surgery.The objective was to know the results of the GTN ointment, so as to avoid surgery, and the probable permanent section of the internal anal sphincter. MATERIAL AND METHODS: Topical Glycerol Trinitrate ointment 0.2% was used twice a day during two weeks. All patients diagnosed with CAF who met the inclusion criteria participated in this study for a one-year period, from February 2007 to January 2008. Two controls were carried out, one at the end of the treatment to verify healing and absence of symptoms, and the other after two months to check recidivism. RESULTS: There were 19 female patients (63.3%) and 11 male patients (36.7%). The average age was 34.87 years, with higher prevalence between 21 and 40 years (50%) and minor prevalence between 41 and 50 years (13.3%). The most frequent symptoms found were the association of anal pain with rectal bleeding in 66.6% of the patients, followed by isolated rectal bleeding and anal pain in 23.3% and 10% of cases, respectively. The most common localization of the CAF was the posterior midline in 63.3% of patients, followed by the anterior midline in 16.7% of patients, and by both midlines in 16.7% of cases. Four of the 30 patients included were lost. All the symptoms vanished in 73% (19)of the 26 remaining patients and symptoms persisted to a lower degree in 27% (7).Headache was an adverse effect in three patients. The control performed after 2 weeks of treatment evidenced partial and complete cicatrization of the fissure in 22 patients (84.6%) and persistence in 4 patients (15.4%). The final control performed after 2 months on the 18 patients who attended evidenced healing of the fissure in 16 (69.6%) and recidivism in 2 (8.7%). CONCLUSIONS: The following conclusion was drawn topical Glycerol Trinitrate 0.2% ointment, applied twice a day during two weeks, is effective in the treatment of chronic anal fissure, with a 69.9% success rate after two months of follow-up. Consequently, it must be considered as an alternate therapy in the treatment of CAF.