Objective: To evaluate the antiinflammatory effect of the association dexamethasone with diclofenac and the association dexamethasone with ketorolac in mandibular third molar surgery. Material and method: Randomized double blind clinical trial that included 75 patients who were randomly divided into three groups: the DK group received the dexamethasone association with ketorolac; the DD group, the dexamethasone association with diclofenac and the control group D, only dexamethasone; all intramuscularly, thirty minutes before surgery. The anti-inflammatory effect was determined by the evaluation of postoperative pain and swelling. The pain was evaluated by means of the analogous visual scale and the total analgesic consumption. Swelling was assessed by measures of facial swelling and mouth opening. Results: The DD group showed less pain intensity at 4 h, 6 h, 12 h, 24 h and 48 h compared to the other treatment groups (p < 0.05). Total analgesic consumption was significantly lower in the DD group (1.20 ± 0.3) compared to the other treatment groups; p = 0.002. Facial swelling was similar in all study groups (p > 0.05). The DD group showed a significant greater oral opening only at 48 hours postoperatively compared to the other study groups (p = 0.01). Conclusions: The preoperative administration of the dexamethasone association with diclofenac has a significantly greater analgesic activity compared to the preoperative administration of the dexamethasone association with ketorolac. However, there is no significant difference in relation to facial swelling.