Aims: To assess the effects of intra-alveolar application of chlorhexidine gel on the incidence of alveolar osteitis (dry socket) and the severity of postsurgical pain. Methods: A total of 160 impacted mandibular third molars were extracted in 80 patients enrolled in this trial. In each subject, a socket was randomly selected and packed to the crest of the alveolar ridge with a gelatin sponge dressing saturated in 0.2% chlorhexidine gel. The contralateral socket was packed with a dry dressing as the placebo. None of the included patients took antibiotics or analgesics. The occurrence of dry socket and patients' pain levels were assessed at the first and third postoperative days. The data were analyzed using Spearman correlation coefficient, McNemar, Wilcoxon, and chi-square tests. Results: Chlorhexidine gel significantly reduced dry socket incidence from 32.6% to 11.3% (P = .001 [McNemar and chi-square], absolute risk reduction = 21.2%, relative risk reduction = 65.4%, odds ratio = 0.263, relative risk = 0.345). It also significantly relieved postoperative pain on both sides in all the patients (P = .001 [Wilcoxon]) and also in the 54 subjects who did not develop dry socket (P = .001 [Wilcoxon]). Conclusions: Besides decreasing the incidence of dry socket, chlorhexidine gel can reduce postsurgical pain in patients with and without dry socket. Keywords: alveolar osteitis, chlorhexidine, dry socket, impacted teeth, postoperative pain, third molars, tooth extraction