['Paradoxical embolism via persistent foramen ovale (PFO) is suspected to be a frequent cause of stroke in younger patients. We investigated whether the prevalence of the risk factors for venous thrombosis factor V Leiden (FVL) and prothrombin G20210A mutation (PT G20210A) is increased in this group of patients.', 'We examined FVL and PT G20210A mutation in 220 patients (group 1) with cerebral ischemia associated with a PFO and without other etiology, in 196 patients with cerebral ischemia of an etiology other than PFO (group 2), and in 362 healthy subjects (group 3) from the same region in Germany.', 'Heterozygosity for the PT G20210A mutation was more common in group 1 (5.0%) than in group 3 (1.4%; sex- and age-adjusted odds ratio 3.66; 95% CI 1.25-10.75; p = 0.01). By contrast, the mutation was not more common in group 2 (2.6%; odds ratio 1.50; 95% CI 0.42-5.41; p = 0.5). Prevalences of FVL were not different between groups.'] Is prothrombin G20210A mutation , but not factor V Leiden , a risk factor in patients with persistent foramen ovale and otherwise unexplained cerebral ischemia?