In this study we evaluated the efficacy of electro-acupoint stimulation, ondansetron versus placebo for the prevention of postoperative nausea and vomiting (PONV). Patients undergoing major breast surgery under general anesthesia were randomized into active electro-acupoint stimulation (A), ondansetron 4 mg IV (O), or sham control (placement of electrodes without electro-acupoint stimulation; placebo [P]). The anesthetic regimen was standardized. The incidence of nausea, vomiting, rescue antiemetic use, pain, and patient satisfaction with management of PONV were assessed at 0, 30, 60, 90, 120 min, and at 24 h. The complete response (no nausea, vomiting, or use of rescue antiemetic) was significantly more frequent in the active treatment groups compared with placebo both at 2 h (A/O/P = 77%/64%/42%, respectively; P = 0.01) and 24 h postoperatively (A/O/P = 73%/52%/38%, respectively; P = 0.006). The need for rescue antiemetic was less in the treatment groups (A/O/P = 19%/28%/54%; P = 0.04). Specifically, the incidence and severity of nausea were significantly less in the A group compared with the other groups, and in the O group compared with the P group (A/O/P = 19%/40%/79%, respectively). The A group experienced less pain in the postanesthesia care unit, compared with the O and P groups. Patients in the treatment groups were more satisfied with their management of PONV compared with placebo. When used for the prevention of PONV, electro-acupoint stimulation or ondansetron was more effective than placebo with greater degree of patient satisfaction, but electro-acupoint stimulation seems to be more effective in controlling nausea, compared with ondansetron. Stimulation at P6 also has analgesic effects.