In a randomized trial, the preemptive analgesic effect of celecoxib in 110 infertile women undergoing day-case diagnostic laparoscopy was studied at King Chulalongkorn Memorial Hospital, Bangkok, Thailand. The patients randomly received either 200 mg celecoxib or placebo orally 2 hours before diagnostic laparoscopy. The post-operative shoulder pain and wound pain were self assessed and recorded, using Visual Analogue Scores (VAS) at 1, 2, 4, 12, and 24 hours. Total post-operative analgesic requirements were recorded at 24 hours. The mean Visual Analogue Scores (VAS) of shoulder pain in celecoxib group was statistically lower than those of the placebo group (p = 0.04). Nevertheless, the mean VAS of wound pain and the total post-operative analgesic requirements were not significantly different. It was concluded that the preemptive celecoxib in day-case diagnostic laparoscopy might have the advantage of decreasing post laparoscopic shoulder pain.