BackgroundThe Cerebrovascular Antiplatelet Trialists' Collaborative Group was formed to obtain and analyze individual patient data from the major randomized trials of common antiplatelet regimens after cerebral ischemia. Although the risk of stroke can be reduced by antiplatelet drugs, there continues to be uncertainty about the balance of risk and benefits of different antiplatelet regimens for an individual patient. AimsOur aim is to provide clinicians with a thorough evidence-based answer on these therapeutic alternatives. MethodsWe have identified six large randomized trials and plan to meta-analyze the data on an individual patient level. In total, these trials have enrolled 46948 patients with cerebral ischemia. Uniquely, the Cerebrovascular Antiplatelet Trialists' Collaborative Group has secured access to the individual data of all of these trials, with the participation of key investigators and pharmaceutical companies. Our principal objective includes deriving a reliable estimate of the efficacy of different antiplatelet regimens on key outcomes including serious vascular events, major ischemic events, major bleeding, and intracranial hemorrhage. ResultsWe propose to redefine composite outcome events, if necessary, to achieve comparability. Further, we aim to build and validate prognostic models for the risk of major bleeding and intracranial hemorrhage and to build a decision model that may support evidence-based decision making about which antiplatelet regimen would be most effective in different risk groups of patients. ConclusionsThis paper outlines inclusion criteria, outcome measures, baseline characteristics, and planned statistical analysis.