Introduction: Venous thromboembolism (VTE) is a common complication in surgical patients, especially those undergoing lower limb orthopaedic procedures as well as oncological resectional surgery. Numerous studies have evaluated the role of acetylsalicylic acid (ASA, aspirin) in primary VTE prevention, with contradictory results reflected in divergent guidelines. We reviewed current evidence for ASA as primary VTE prophylaxis.Methods: English language studies meeting our inclusion criteria were retrieved from PubMed, EMBASE and Cochrane databases. Six studies (3 meta-analyses and 3 randomized trials) comparing ASA with placebo and 7 studies (1 meta-analysis, 5 randomized trials, and 1 prospective) comparing ASA with other anticoagulants were included in the final analysis. Retrospective studies and case reports were excluded.Results: ASA is more effective than placebo in primary VTE prevention. Although there is clinical equipoise when ASA is compared with other anticoagulants, studies specific to orthopaedic surgery suggest that ASA appears as effective as low molecular weight heparin (LMWH) and may reduce bleeding risk. Extended prophylaxis up to 4 weeks post surgery reduces VTE episodes.Conclusions: ASA may be considered as a potential strategy in primary VTE prophylaxis in orthopaedic patients at high-risk of bleeding complications. Further studies comparing ASA with LMWH/oral anticoagulants in primary thromboprophylaxis following non orthopaedic surgery are warranted. (C) 2015 Royal College of Surgeons of Edinburgh (Scottish charity number SC005317) and Royal College of Surgeons in Ireland. Published by Elsevier Ltd. All rights reserved.