Aim: To evaluate the preemptive analgesia of ketoprofen in comparison with diclofenac after mandibular third molar surgery. Methods: This study was a double-blind, randomized clinical trial. Forty patients were randomized into two treatment groups (each with 20 patients) by using a series of random numbers: group A received ketoprofen 100 mg and group B received diclofenac 75 mg, all intramuscularly. Surgery was done 30 minutes after analgesic treatments. The durations of analgesia, pain intensity, analgesic consumption, and side effects were evaluated. The statistical analysis was done using the chi-square, Student t, Mann-Whitney U, and Log-Rank tests. Results: The duration of analgesia was longer in the ketoprofen group when compared with the diclofenac group. The number of patients taking the first rescue analgesic at 6 hours was lower in the ketoprofen group in comparison with the diclofenac group. Patients who received ketoprofen had lower pain intensity compared with patients who received diclofenac. Conclusion: Intramuscular ketoprofen 100 mg is more effective than intramuscular diclofenac 75 mg after mandibular third molar extraction when used as a preemptive analgesic. Palabras clave: dental pain, diclofenac, ketoprofen, third molar surgery