Objectives: The aim of the present double-blind, randomized, controlled clinical trial was to evaluate the effect of ketorolac buccal infiltration of on postendodontic pain of patients with symptomatic irreversible pulpitis in mandibular first/second molars. Method and materials: Sixty patients meeting the inclusion criteria were evaluated. After receiving a standard inferior alveolar nerve block (IANB) followed by a buccal infiltration injection with lidocaine, half of the participants randomly received a supplemental buccal infiltration of 30 mg/mL ketorolac tromethamine and the other half received a buccal infiltration of normal saline adjacent to the periapical region of the tooth being treated. Afterwards, all participants received a single-visit root canal treatment. Pre- and postoperative (immediately after treatment, and at 2, 4, 6, and 24 hours) pain levels were evaluated via Heft-Parker visual analog scale (HP-VAS). Analgesic consumption was also recorded. The data were statistically analyzed using repeated-measures ANOVA and Friedman tests. The significance level was set at P .05. Results: There was a significant difference in postoperative pain between the two groups in overall evaluations and in each time interval (P .001 and P = .043 respectively). Of those patients receiving ketorolac, 60% (18/30) did not require any analgesic consumption up to 24 hours postoperatively, whereas this number was 43% (13/30) for the placebo group. Conclusion: Ketorolac buccal infiltration could reduce the postoperative pain experienced by patients requiring endodontic treatment diagnosed with symptomatic irreversible pulpitis. Keywords: buccal infiltration, ketorolac, nonsteroidal anti-inflammatory drug, pain, root canal treatment