Dexamethasone has antiemetic and analgesic effects in various types of surgery. In a randomized, double-blind, placebo-controlled trial, we evaluated the efficacy of dexamethasone for reducing postoperative nausea and vomiting (PONV) and analgesic requirement in women undergoing general anesthesia for mastectomy. Patient were allocated randomly to one of three groups (n=30 of each) to receive intravenously either placebo or dexamethasone at two different doses (4 mg, 8 mg) at the end of surgery. Postoperatively, emetic episodes and analgesic requirement were evaluated by an investigator. Patient demographics and types of surgery were not different among the treatment groups. The rate of patients experiencing PONV during 0-24 hours after anesthesia was 33% with dexamethasone 4 mg (p=0.01) and 27% with dexamethasone 8 mg (p=0.002), compared with placebo (67%). The need of indomethacin for intolerable pain was less in patients who had received dexamethasone 8 mg than in those who had received placebo (p=0.001) or dexamethasone 4 mg (p=0.034). No difference in analgesic requirement was found between the dexamethasone 4 mg and placebo groups (p=0.18). No clinically serious adverse events attributed to the study drug were observed in any of the groups. We conclude that dexamethasone 8 mg effectively decreases PONV and analgesic requirement in women undergoing general anesthesia for mastectomy.