The efficacy and tolerability of diclofenac suppositories given pre and/or post-operatively were investigated in a randomized double-blind study on 99 patients undergoing tonsillectomy. In one group, 50 mg diclofenac was given 1 h preoperatively, followed by 50 mg directly after the operation. In another group, diclofenac 100 mg was given only immediately post-operatively. A significantly lower consumption of rescue analgesics (paracetamol and/or pethidine) was found in the group treated preoperatively with diclofenac and the average time until first demand of rescue analgesics was significantly longer compared to the group given diclofenac post-operatively only. The tolerance was good and no serious bleeding complications occurred in either group. In the treatment of post-operative pain after tonsillectomy, the combination of pre and post-operative administration of diclofenac suppositories resulted in significantly lower consumption of rescue analgesics and is thus preferable to administration solely post-operatively.