Up to 40% of acute ischaemic strokes in young adults are cryptogenic in nature, that is, no cause is determined. In more than half of these patients, patent foramen ovale (PFO) is seen along with an increased incidence of atrial septal aneurysm. The commonest method of investigation is echocardiography (preferably transoesophageal echocardiography). On the basis of available evidence, low risk patients are treated with antiplatelet agents and high risk patients with warfarin. There are inconclusive data on the efficacy of PFO closure to prevent stroke recurrence. However, if there is recurrent stroke or intolerance to medical therapy, percutaneous closure is carried out.