BACKGROUND: In patients with acute ischaemic stroke, platelets become activated. Antiplatelet therapy might reduce the volume of brain damaged by ischaemia and reduce the risk of early recurrent ischaemic stroke. This might reduce the risk of early death and improve long-term outcome in survivors. However, antiplatelet therapy might also increase the risk of fatal or disabling intracranial haemorrhage. OBJECTIVES: The aim of this review is to assess the efficacy and safety of antiplatelet therapy in acute ischaemic stroke. SEARCH STRATEGY: We searched the Cochrane Stroke Group Trials Register (last searched August 2002), the Cochrane Controlled Trials Register (CCTR) (Cochrane Library Issue 1 2002), MEDLINE (June 1998-October 2001), and EMBASE (June 1998-February 2002). In 1998, for previous versions of this review, we searched the register of the Antiplatelet Trialists Collaboration, MedStrategy and contacted relevant drug companies. SELECTION CRITERIA: Randomised trials comparing antiplatelet therapy (started within 14 days of the stroke) with control in patients with definite or presumed ischaemic stroke. DATA COLLECTION AND ANALYSIS: Two reviewers independently applied the inclusion criteria and assessed trial quality, and for the included trials, extracted and cross-checked the data. MAIN RESULTS: Nine trials involving 41,399 patients were included. Two trials testing aspirin 160 to 300 mg once daily started within 48 hours of onset contributed 98% of the data. The maximum follow-up was six months. With treatment, there was a significant decrease in death or dependency at the end of follow-up (OR = 0.94; 95% CI 0.91 to 0.98). In absolute terms, 13 more patients were alive and independent at the end of follow-up for every 1000 patients treated. Furthermore, treatment increased the odds of making a complete recovery from the stroke (OR = 1.06; 95% CI 1.01 to 1.11). In absolute terms, 10 more patients made a complete recovery for every 1000 patients treated. Antiplatelet therapy was associated with a small but definite excess of 2 symptomatic intracranial haemorrhages for every 1000 patients treated, but this was more than offset by a reduction of 7 recurrent ischaemic strokes and about one pulmonary embolus for every 1000 patients treated. REVIEWER’S CONCLUSIONS: Antiplatelet therapy with aspirin 160 to 300 mg daily, given orally (or per rectum in patients who cannot swallow), and started within 48 hours of onset of presumed ischaemic stroke reduces the risk of early recurrent ischaemic stroke without a major risk of early haemorrhagic complications and improves long-term outcome.