An objective evaluation study was carried out on necrotic pulp of the maxillary central incisors in order to describe the incidence of post-operative pain following single-visit root canal treatment using three different instrumentation techniques. One hundred and five teeth from 91 patients whose ages ranged from 18 to 55 years were selected and divided into three groups. Each group (35 teeth) was prepared by one of the following instruments: stainless steel k-files utilizing a step-back technique, Profile 0.04-29% series files using crown-down pressureless technique and Profile GT files using crown-down pressureless technique. A statistically significant difference in the incidence of post-operative pain within the first 48 hours after the completion of root canal therapy was observed among the groups. It was concluded that the use of Profile 0.04-29% taper and Profile GT files contributed to the lower incidence of post-operative pain in patients who received root canal therapy in single endodontic visit.