INTRODUCTION: Initial orthograde root canal therapy (RCT) is used to treat dentoalveolar pathosis. The effect RCT has on pain intensity has been frequently reported, but the effect on other dimensions of pain has not. Also, the lack of large prospective studies involving diverse groups of patients and practitioners who are not involved in data collection suggest that there are multiple opportunities for bias to be introduced when these data are systematically aggregated. METHODS: This prospective observational study assessed pain intensity, duration, and its interference with daily activities among RCT patients. Sixty-two practitioners (46 general dentists and 16 endodontists) in the National Dental Practice-Based Research Network enrolled patients requiring RCT. Patient-reported data were collected before, immediately after, and 1 week after treatment using the Graded Chronic Pain Scale. RESULTS: The enrollment of 708 patients was completed over 6 months with 655 patients (93%) providing 1-week follow-up data. Before treatment, patients reported a mean (+/-standard deviation) worst pain intensity of 5.3 +/- 3.8 (0-10 scale), 50% had "severe" pain (>/=7), and mean days in pain and days pain interfered with activities were 3.6 +/- 2.7 and 0.5 +/- 1.2, respectively. After treatment, patients reported a mean worst pain intensity of 3.0 +/- 3.2, 19% had "severe" pain, and mean days in pain and days with pain interference were 2.1 +/- 2.4 and 0.4 +/- 1.1, respectively. All changes were statistically significant (P < .0001). CONCLUSIONS: RCT is an effective treatment for patients experiencing pain, significantly reducing pain intensity, duration, and related interference. Further research is needed to reduce the proportion of patients experiencing "severe" postoperative pain.