Introduction: This prospective, single-center, single-blind, randomized controlled trial aimed to evaluate whether maintaining apical patency (AP) during endodontic treatment increases postoperative pain in molar teeth with necrotic pulp and apical periodontitis. Methods: Three hundred twenty qualified patients between 21 and 45 years of age were randomized into 1 of 2 groups (the AP group and the nonapical patency [NAP] group) using a series of random numbers in a 1:1 ratio. Qualified patients were selected from patients who had necrotic pulp and apical periodontitis in the maxillary or mandibular molar teeth. The primary outcome was to assess postoperative pain severity, and the secondary outcome was to evaluate analgesic consumption during the 7-day follow-up period using the visual analog scale (VAS). The VAS consisted of a 100-mm line. Pain severity was evaluated as no pain (0-4 mm), mild pain (5-44 mm), moderate pain (45-74 mm), and severe pain (75-100 mm). The Student t test was used to identify statistically significant differences between the study groups (P < .05). Results: The mean VAS scores were significantly lower in the AP group in the first 5 postoperative days (P < .05); after which, it was nonsignificant. In the NAP group, the postoperative pain increased between 12 and 24 hours, whereas the postoperative pain decreased in the AP group during that period. At 12 and 24 hours, the mean VAS scores for the AP group were 42.90 and 37.78 mm, respectively. The mean VAS scores for the NAP group were 64.46 and 65.74 mm, respectively. None of the patients had severe postoperative pain during the follow-up period. No significant difference was found in analgesic consumption (P > .05) between the groups. Conclusions: The maintenance of AP in molar teeth with necrotic pulp and apical periodontitis was associated with less postoperative pain when compared with NAP.