Twin and family-based studies indicate that genetic factors might be involved in the risk of transient ischemic attack (TIA) and ischemic stroke (IS). Identification of genetic risk factors for new vascular events after cerebral ischemia may target secondary prevention. The overall aim of POLARIS is to study which polymorphisms predispose to new vascular events after TIA/IS and to assess their predictive value. Patients who have had a TIA or IS of presumed arterial origin are included. The study design is twofold. In part one the prevalences of polymorphisms will be compared between 300 long-term survivors of the Dutch TIA Trial (average follow-up 10 years) and 820 patients with recent TIA/IS. In part two a cohort of 820 patients with recent TIA/IS will be followed for the occurrence of vascular events for an average of 3.5 years. Several polymorphisms of interest will be genotyped, including factor V Leiden, prothrombin 20210A, 5,10-methylenetetrahydrofolate reductase, HR2 haplotype factor V and factor XIII Val34Leu.