Objective: To evaluate the analgesic effect of the administration of the association of diclofenac with B vitamins in patients undergoing elective mandibular third molar surgery. Material and method: Randomized controlled double blind clinical trial that included 70 patients divided into 2 groups, one group received diclofenac plus B vitamins (experimental) and the other only diclofenac (control). The main variable was pain intensity according to visual analog scale (VAS) after 1, 3, 6, 9, 12 and 24 hours after the surgery was completed; the secondary variables were the time for rescue analgesia and the total consumption of analgesics in the postoperative period. Results: The pain intensity was increased in both groups until 6 hours (p > 0.05). At 24 hours, the highest pain intensity was perceived in both study groups, being significantly lower in the experimental group (3.21 ± 1.31) compared to the control group (4.89 ± 1.42); p = 0.035. The time for rescue analgesia was significantly higher in the experimental group (11.32 ± 2.31 hours) compared to the control group (8.93 ± 1.91 hours); p = 0.001. The total analgesic consumption was lower in the experimental group (6.17 ± 1.42 tablets) compared to the control group (6.49 ± 0.97 tablets); p = 0.10. Conclusion: The administration of the association of diclofenac with vitamins B showed a greater analgesic effect compared to only diclofenac in patients undergoing elective mandibular third molar surgery.