Principles: Alveolar osteitis (dry socket) is the most common complication following the extraction of permanent teeth. This study was undertaken to compare the effect of two chlorhexidine rinse protocols on the incidence of alveolar osteitis in patients undergoing surgical removal of impacted mandibular third molar teeth. Methods: A prospective randomized clinical trial was conducted among 99 subjects. Patients were randomly assigned into two groups. Subjects were instructed to rinse twice daily with 15 ml of chlorhexidine rinse 30 seconds for one week before and one week after surgery (group I) or one week after surgery (group II). Postoperatively, all patients were instructed to return in one week or sooner if bothersome pain increased or persisted. Data were collected regarding abnormal healing, presence of necrotic tissue, exposed bone, and absence of clot. Results: The results indicated group I and group II were not statistically significant different in the reduction of alveolar osteitis. Conclusions: To reduce alveolar osteitis after impacted third molar surgery, it was observed use of postoperative chlorhexidine rinse was adequate. The postoperative use of chlorhexidine is more feasible than both preoperative and postoperative use.