Although therapy with acetylsalicylic acid (aspirin, ASA) is well established in secondary prevention of stroke, efficacy and side effects of this substance in acute stroke treatment are undetermined. ASA may be useful in acute cerebral ischemia because of its potential to prevent thrombus propagation and neuronal damage. A total of 268 patients with an acute cerebral ischemia, who were admitted to our stroke unit within 24 hours after stroke, were treated with intravenously administered ASA (0.5 g/day) in combination with low-dose heparin. The functional status of the patients was assessed after 1 month using the modified Rankin Scale. Eighteen (6.7%) patients died during the observation period. The functional status according to Rankin Scale was classified as stage 0 in 76 (28.3%), 1 in 59 (22.0%), 2 in 39 (14.6%), 3 in 32 (12.3%), 4 in 36 (13.4%), and 5 in 7 (2.6%) patients. A symptomatic secondary intracerebral hemorrhage was seen in one patient. Gastrointestinal symptoms were observed in 13 (4.8%) patients, including five instances of gastrointestinal bleeding. Further complications were allergic reactions to aspirin (one) and hematuria (one). Recurrent cerebral ischemia occurred in nine (3.3%) patients (five with transient ischemic attack or minor stroke) during the observation period. We conclude that treatment of acute ischemic stroke with intravenously applied aspirin in combination with low-dose heparin is safe. Efficacy of this therapy should be elucidated in a controlled trial.