Introduction: There has been long-standing controversy on root canal treatment protocol with regard to single- and multiple-visit endodontic therapy. Amongst other factors, the question stands with regard to the amount of postoperative pain associated with single- and multiple-visit therapy. This is especially true in cases with periapical lesions. Aim: The aim of this split-mouth study was to determine the difference in postoperative pain associated with single- and multiple-visit root canal therapy and to determine if different instrumentation techniques were associated with different amounts of postoperative pain. Materials and methods: Thirty patients with bilateral apical periodontitis indicated for root canal therapy and were treated with single-visit therapy on one side and multiple-visit therapy on the other side. Their postoperative pain was measured using the visual analogue pain scale on 1, 3 and 7 days after the treatment. Out of the 30 patients, 10 were treated using the ProTaper Universal files, 10 using Hero Shaper and 10 using the Self-adjusting File. Results and conclusion: Analysis of postoperative pain in single- and multiple-visit therapy was carried out using the Student's t test and analysis of postoperative pain associated with the different instruments used in single-visit and multiple-visit, respectively, was calculated using the one-way analysis of variance. There was no statistically significant difference (P > 0.05) in postoperative pain of single and multiple root canal treatments. There was no difference in postoperative pain between the three different instrumentation techniques used (P > 0.05). Schlagwörter: Hero Shaper, multiple-visit therapy, postoperative pain, ProTaper Universal, Selfadjusting File