Background <p>Postoperative pain following endodontic treatment is a significant and common issue in daily clinical practice, frequently studied, and a source of concern for both patients and clinicians.</p> Aim <p>This study aimed to evaluate postoperative pain and analgesic use after single-visit endodontic treatment with a reciprocating system with or without foraminal enlargement in mandibular molars with necrosis and apical periodontitis.</p> Methods <p>Sixty patients undergoing endodontic treatment on mandibular molars were divided into two groups (<i>n</i> = 30): with foraminal enlargement (FE), with the working length set at 0.0 mm from the apex, and the other group without foraminal enlargement (WFE) at 1.0 mm short of the apex. Instrumentation was performed with the Wave One Gold System in a single-visit, rinsed with 2.5% sodium hypochlorite, and filled with a single cone and AH -Plus sealer. The patients were requested to rate their pain at 24, 48, 72 h, and 1 week on a visual analog scale (VAS) as nonexistent, mild, moderate, or severe, as well as to indicate the need for oral analgesics. The number of participants reporting pain was similar at both 24 and 48 h (<i>p</i> &gt; 0.05).</p> Results <p>Mean VAS scores were low in both groups at all time points, with no clinically meaningful between-group differences. At 72 h and 7 days, no participant in either experimental group reported pain. There was no statistically significant difference in the painkiller tablets taken between the experimental groups at any evaluated period.</p> Conclusion <p>The frequency of postoperative pain and the number of analgesics taken by the patients were similar in the two experimental groups.</p>