In broad, relatively unselected patients with acute ischaemic stroke, immediate high-dose anticoagulation therapy to avert early stroke progression or recurrence reduces recurrent ischaemic stroke compared with control during the treatment period but this benefit is offset by an increase in intracranial haemorrhage (ICH) and extracranial haemorrhage (ECH). Immediate antiplatelet therapy has similarly efficacy as anticoagulation in averting early stroke progress or recurrence, and is safer when used as an immediate agent (see Chapter 9). In acute ischaemic stroke patients with atrial fibrillation, after start of antiplatelet therapy on presentation, early switchover to anticoagulation therapy 2 -14 days after stroke onset is reasonable, but caution should be taken in certain subgroups of patients with high risk of bleeding. In broad, relatively unselected ischaemic stroke patients, low-dose, venous prophylaxis anticoagulation compared with control reduces the occurrence of asymptomatic deep venous thrombosis (DVT) and shows a tendency to reduce pulmonary embolism, but also shows off-setting tendencies to increase ICH and ECH, without conferring a clear net clinical benefit. Low-molecular-weight heparins (LMWH) or heparinoids, compared with unfractionated heparin, appear to further decrease the occurrence of DVT and PE but potentially further increase ICH, but there are too few data to provide reliable information.