Background and Purpose— Many randomized clinical trials have evaluated the benefit of long-term use of antiplatelet drugs in reducing the risk of new vascular events in patients with a recent transient ischemic attack or ischemic stroke. Evidence from these trials forms the basis for national and international guidelines for the management of nearly all such patients in clinical practice. However, abundant and strict enrollment criteria may limit the validity and the applicability of results of randomized clinical trials to clinical practice. We estimated the eligibility for participation in landmark trials of antiplatelet drugs of an unselected group of patients with stroke or transient ischemic attack from a national stroke survey. Methods— Nine hundred seventy-two patients with transient ischemic attack or ischemic stroke were prospectively and consecutively enrolled in the Netherlands Stroke Survey. We applied 7 large antiplatelet trials’ enrollment criteria. Results— In total, 886 patients were discharged alive and available for secondary prevention. Mean follow-up was 2.5 years. The annual rate of transient ischemic attack, stroke, or nonfatal myocardial infarction was 6.7%. The proportions of patients fulfilling the trial enrollment criteria ranged from 25% to 67%. Mortality was significantly higher in ineligible patients (27% to 41%) than in patients fulfilling enrollment criteria (16% to 20%). Rates of vascular events were not higher in trial-eligible patients than in ineligible patients. Conclusions— Our data confirm that patients with ischemic attack and stroke enrolled in randomized clinical trials are only partially representative of patients in clinical practice. Use of less strict enrollment criteria could enhance “generalizability” and result in more efficient selection of patients for randomized clinical trials.