Laparoscopic tubal ligation is associated with an appreciably high rate of postoperative nausea and vomiting. This study was designed to compare the effectiveness of ondansetron, dexamethasone, ondansetron plus dexamethasone or placebo in the prevention of postoperative nausea and vomiting in patients after laparoscopic tubal ligation. In a prospective, randomised, double blind placebo controlled trial, 160 ASA I-II females received one of four regimens; ondansetron 4 mg, dexamethasone 8 mg, ondansetron 4 mg plus dexamethasone 8 mg or placebo (n=40 each) intravenously immediately before induction of anaesthesia. Patients were then observed for 24 hours postoperatively. The incidence of emetic episodes in the ondansetron with dexamethasone group was lower than in the placebo (p<0.001) and ondansetron (p=0.091) and dexamethasone (p=0.143) groups. A complete response (as no postoperative nausea and vomiting) was achieved in 60% of patients given ondansetron, 63% of the patients given dexamethasone, 78% of patients given ondansetron with dexamethasone and 37% of patients received placebo. The prophylactic use of ondansetron with dexamethasone is more effective in preventing postoperative nausea and vomiting.