['Electrical acustimulation can reduce postoperative nausea and vomiting (PONV). The primary purpose of this study was to investigate the effectiveness of acustimulation in relation to known risk factors for PONV. We also tested the secondary hypothesis that pre- or post-induction application of acustimulation results in differences in PONV reduction.', 'Two hundred women undergoing vaginal hysterectomy were enrolled in this prospective, observer-blind, randomized controlled trial. Patients received randomly for 24 h acustimulation (n=101), subdivided into groups of pre-induction (n=48) and post-induction (n=53), or sham stimulation (n=99), subdivided into groups of pre-induction (n=49) or post-induction (n=50). Nausea and vomiting/retching was recorded for 24 h after operation in the whole group and stratified by risk factors (female gender, non-smoker, history of PONV/motion sickness, and postoperative morphine usage).', 'The incidence of PONV and need for rescue therapy was significantly lower in the acustimulation than in the sham group (PONV, 33% vs 63%, P<0.001; rescue therapy, 39% vs 61%, P=0.001). The risk ratio for acustimulation and PONV was 0.29 [95% confidence interval (CI) 0.16-0.52] and for rescue therapy, it was 0.38 (95% CI 0.21-0.66). Subgroup analyses according to the simplified risk score by Apfel and colleagues revealed a reduction in high-risk patients, that is, when three or four risk factors were present. Binary logistic regression analysis revealed that no history of PONV and usage of acustimulation were independent predictors for risk reduction of all PONV qualities. No significant difference in PONV reducing effects could be detected between pre- and post-induction.'] Does p6 acustimulation effectively decrease postoperative nausea and vomiting in high-risk patients?