The impact of body mass index (BMI) on postoperative nausea and vomiting (PONV) is controversial, and few studies have focused on their relationship. We investigated the effects of BMI on PONV, taking into account other PONV risk factors. We analyzed adults over the age of 18 years who received general anesthesia between 2015 and 2019, using propensity score matching. Before propensity score matching, odds ratios (ORs) for PONV were lower for overweight (OR, 0.91 / 95% confidence interval (CI), 0.87&ndash / 0.96 / p < / 0.0001) or obese patients (OR, 0.77 / 95% CI, 0.71&ndash / 0.84 / p < / 0.0001) than for normal-BMI patients. After matching, the ORs for PONV of overweight (OR, 0.89 / 95% CI, 0.80&ndash / 0.98 / p = 0.016) and obese patients (OR, 0.71 / 95% CI, 0.63&ndash / 0.79 / p < / 0.0001) were low. However, the ORs of underweight patients did not differ from those of normal-BMI patients, irrespective of matching. Therefore, the incidence of PONV may be lower among adults with a higher‑than‑normal BMI.