Aims The bleeding risk of current antithrombotic strategies in clinical settings, including recently developed agents, needs to be clarified. Methods and Design In an investigator-initiated, prospective, multicentre, observational study, patients with cerebrovascular or cardiovascular diseases who were taking oral antiplatelet or anticoagulant agents were enrolled. Compulsory multimodal magnetic resonance images were acquired at baseline to assess cerebral small vessel disease. Six-month follow-up will be performed for two years. The primary outcome is major bleeding as defined by the International Society on Thrombosis and Hemostasis. Results Between October 2016 and March 2019, 5306 patients (71.7 ± 11.2 years old, 1762 women) were enrolled. Previous intracranial haemorrhage was documented in 181 patients (3.4%), cerebrovascular disease (including asymptomatic) requiring antithrombotic therapy in 5006 patients (94.3%), and atrial fibrillation in 1061 patients (20.0%). At entry, 3726 patients (70.2%) were taking antiplatelet agents alone, including 551 (10.4%) using dual antiplatelet agents, 1317 (24.8%) taking anticoagulants alone, and the remaining 263 (5.0%) taking both. The leading antiplatelet agent was clopidogrel (2014 patients), and the leading combination of dual antiplatelet medication was clopidogrel plus aspirin (362). Use of direct oral anticoagulants (1029 patients, 19.4%) exceeded warfarin use (554, 10.4%). The number of pivotal bleeding events exceeded 200 in April 2020. Conclusions This study is expected to provide the incidence of bleeding complications of recent oral antithrombotics in clinical practice and identify their associations with underlying small vessel disease and other biomarkers. Novel risk stratification models for bleeding risk will be able to be created based on the study results.