['Although buprenorphine sometimes causes severe emesis, its relation to the menstrual cycle has not been reported.', 'We conducted a prospective study on 68 reproductive-age women following lower extremity surgery under epidural anesthesia plus buprenorphine, to assess the effect of the day of the menstrual cycle on the incidence of postoperative nausea and vomiting. The patients were divided according to the phase of the menstrual cycle into four groups: day 1-7 group, day 8-14 group, day 15-24 group and day 25 to end of the cycle group.', 'Nausea and vomiting were reported in 46 patients (67.6%), and the incidence was higher in the day 25 to end of the cycle group than in the day 8-14 or day 15-24 groups, and higher in the day 1-7 group than in the day 8-14 group.'] Does menstrual stage influence postoperative nausea and vomiting following epidural buprenorphine?