Antithrombotic drugs belong to the most used medications in healthcare. About one in ten Dutch inhabitants uses them. Antithrombotic drugs reduce the risk of clot formation caused by pathologies such as atrial fibrillation or venous thromboembolism. Mitigating this risk comes at the cost of a small increase in the risk of bleeding. Often this trade-off is clear-cut and favours the use of antithrombotic drugs. However, in some cases these drugs can result in adverse events. Antithrombotic related adverse events (ARAEs) gained increasing attention in adverse event studies in the Netherlands in the past decades but the exact magnitude remained unknown. This thesis aims to systematically measure the safety of antithrombotic care provided in Dutch hospitals to guide future improvement efforts. The following research questions are discussed: 1) How common are (preventable) antithrombotic related adverse events in Dutch hospitals and what are the circumstances in which they occur? In our research we found that ARAE incidence in deceased patients decreased from 1.20% in 2008 to 0.54% in 2015/2016. Although this is an encouraging result, other findings were concerning. These are: a lacking decline of ARAEs in discharged patients, the relatively high preventability of ARAEs (28.54%) and the increasing trend of involvement of antiplatelet and/or combined antithrombotic therapy in ARAEs over time. 2) How reliable is perioperative antithrombotic management (PAM) and administering VTE prophylaxis in Dutch hospitals? Reliability was operationalised as guideline compliance in this thesis. We concluded that deviations from antithrombotic guideline recommendations were common. Most of these recommendations can be regarded as process measures. When comparing them as such with measures from other clinical domains, compliance is low. Additionally, we observed significant variation in compliance, up to 70 percentage points, between hospitals. This is indicative of a heterogeneous adoption of antithrombotic CPG recommendations in ...