Hereditary and acquired coagulation disorders may play an important role in the pathophysiology of acute ischaemic stroke. Because of the low prevalence of these disorders and the considerable costs of unmindful diagnostic effort, a custom-tailored approach is desirable. Suggestive in favour of a possible prothrombotic clotting disorder are young patients, repeated episodes of thrombosis in the patient's history, inappropriate atherosclerotic vascular changes, previous repeated miscarriages in stroke patients, or structural cardiac abnormalities as a patent foramen ovale. Disorders affecting antithrombin III, protein C und S, APC-resistance, the prothrombin mutation, homocysteinaemia, antiphospholipid antibodies, and procoagulatory cellular interaction are discussed.