Objective: To determine the antiinflammatory effectiveness of dexamethasone plus complex B in lower third molar surgery. Methods: The present study is a double-blind randomized controlled trial of parallel design. It was carried out in the Stomatologic Clinic of the Universidad Privada Antenor Orrego (UPAO) of Trujillo during 2010. The sample consisted of 36 patients randomly divided into two groups. Each patient signed an informed consent. One hour prior to surgery, an intramuscular dose of dexamethasone and an intramuscular dose of dexamethasone plus complex B were administered to the control group (A). The anti-inflammatory effect was determined by the horizontal measurement of the intersection of the dots anatomical: tragus-white tissue pogonion and gonion-external angle of the eye. Measurements were performed at 24, 48 and 96 hours after surgery. Results: When comparing the groups, it was observed that the administration of dexamethasone plus B complex showed a lower postoperative inflammation than that of dexamethasone alone at 24, 48 and 96 hours (p = 0.03; p = 0.002; p = 0.001). The pivotal results were observed for males (p = 0.01), females (p = 0.00001), those under 25 years (p = 0.011) and greater than or equal to 25 years (p = 0.029). Conclusion: Intramuscular administration of dexamethasone plus B complex prior to third molar surgery produces less post-operative inflammation and is independent of gender and age.