Pre-emptive analgesic efficacy of the non-steroidal anti-inflammatory drug, diclofenac sodium, was tested in 21 young, fit, patients undergoing third molar extractions in a double-blind, randomised, cross-over, trial. Pain scores and mouth opening were observed for 1 week after the operation and these did not show any differences following pre- and postoperative oral administration of diclofenac sodium 100 mg (P>0.05). There sere no differences in the patients' preference for the two methods of treatment (P>0.05). The study suggests that the non-steroidal anti-inflammatory drug diclofenac sodium does not cause any significant pre-emptive analgesic effects in the dose administered.