Long-acting neuraxial opioids provide excellent analgesia after surgery, but are associated with higher rates of postoperative nausea and vomiting. Dexamethasone effectively prevents postoperative nausea and vomiting after general anaesthesia, but its value in patients receiving long-acting neuraxial opioids is undetermined. Therefore, the objective of this meta-analysis was to assess the prophylactic anti-emetic efficacy of intravenous (i.v.) dexamethasone in this population. The study methodology followed the PRISMA statement guidelines. The primary outcome was the need for rescue anti-emetics during the first 24 postoperative hours, analysed according to the dose of dexamethasone (low-dose 2.5-5.0 mg; intermediate dose 6.0-10.0 mg), timing of administration (beginning or end of surgery) and route of long-acting opioid administration (intrathecal or epidural). Additionally, the rates of complications (restlessness, infection, hyperglycaemia) were sought. Thirteen trials were identified, representing a total of 1111 patients. When compared with placebo, intravenous dexamethasone reduced the need for rescue anti-emetics (risk ratio (95%CI) 0.44 (0.35-0.56); I ² = 43%; p < 0.00001; quality of GRADE evidence: moderate), without differences between dexamethasone doses (p for sub-group difference = 0.67), timing of administration (p for sub-group difference = 0.32) or route of long-acting opioid (p for sub-group difference = 0.10). No patients developed infection or restlessness among trials that sought these complications. No trial measured blood glucose levels. In conclusion, there is enough evidence to state that intravenous dexamethasone provides effective anti-emetic prophylaxis during the first 24 postoperative hours in patients who receive long-acting neuraxial opioids.