BACKGROUND: Although the use of postoperative opioids is a well-known risk factor for postoperative nausea and vomiting (PONV), few studies have been performed on the effects of intraoperative opioids on PONV. We examined the effects of a single bolus administration of fentanyl during anesthesia induction and the intraoperative infusion of remifentanil on PONV. METHODS: Two hundred and fifty women, aged 20 to 65 years and scheduled for thyroidectomy, were allocated to a control group (Group C), a single bolus administration of fentanyl 2 microg/kg during anesthesia induction (Group F), or 2 ng/ ml of effect-site concentration-controlled intraoperative infusion of remifentanil (Group R) groups. Anesthesia was maintained with sevoflurane and 50% N2O. The incidence and severity of PONV and use of rescue antiemetics were recorded at 2, 6, and 24 h postoperatively. RESULTS: Group F showed higher incidences of nausea (60/82, 73% vs. 38/77, 49%; P = 0.008), vomiting (40/82, 49% vs. 23/77 30%; P = 0.041) and the use of rescue antiemetics (47/82, 57% vs. 29/77, 38%; P = 0.044) compared with Group C at postoperative 24 h. However, there were no significant differences in the incidence of PONV between Groups C and R. The overall incidences of PONV for postoperative 24 h were 49%, 73%, and 59% in Groups C, F, and R, respectively (P = 0.008). CONCLUSIONS: A single bolus administration of fentanyl 2 microg/kg during anesthesia induction increases the incidence of PONV, but intraoperative remifentanil infusion with 2 ng/ml effect-site concentration did not affect the incidence of PONV.