Gynaecologic laparoscopic surgeries are associated with significant postoperative nausea and vomiting (PONV). Nitrous oxide as a gaseous anaesthetic has a role in contributing to PONV. This prospective randomised study was carried out to determine the incidence of PONV as the inspired concentration of nitrous oxide increases from 50% to 70%, when compared with a control group receiving 30% oxygen and air in gynaecologic laparoscopic surgeries under general anaesthesia. 165 patients with ASA physical status I and II, aged 18-60 years, scheduled for elective gynaecologic laparoscopic surgery of more than 90 minutes duration, were recruited for the study. The patients were randomly assigned to three groups.The early (0-2 hours), late (2-24 hours) and overall (at the end of 24 hours) incidence of PONV were recorded in all three groups. The severity of nausea was also assessed. Some significant conclusions were drawn at the end of this study.