Summary. This review summarizes available evidence on effects of aspirin on incidence and outcomes of venous thromboembolism (VTE). From a pathophysiological point of view, inhibition of platelet aggregation is associated with an impaired thrombus formation both in an experimental model of venous thrombosis and in vivo. Epidemiological evidence in support of a beneficial effect of acetylsalicylic acid on VTE incidence is provided by the Antiplatelet Trialists’ Collaboration meta-analysis of studies on the use of antiplatelet agents in cardiovascular risk reduction, showing a significant 25% risk reduction of pulmonary embolism. Moreover, a meta-analysis on older trials of antiplatelet agents in postsurgical VTE prevention and the large Pulmonary Embolism Prevention trial demonstrate a protective effect of the same magnitude: 25–30%. However, as low-molecular-weight heparins (LMWH) and vitamin K antagonists (VKA) have shown a superior efficacy and safety profile, and no direct comparisons have been made between aspirin, LMWH and VKA in prolonged use, the most recent guidelines advise against aspirin monotherapy for thromboprophylaxis in the surgical patient. Currently, there is no evidence to support a role for aspirin in air travel-related VTE. Regarding prevention of recurrent VTE, studies are ongoing to determine the potential role of aspirin after a first unprovoked VTE.