Background - Early administration of paracetamol may improve outcome of patients with acute stroke and a baseline body temperature of 37 degrees C or above by lowering body temperature and preventing fever. Besides its antipyretic effects, paracetamol may affect blood pressure through cyclooxygenase-2 inhibition. We therefore aimed to assess the effect of high-dose paracetamol on blood pressure in patients with acute stroke. Methods - We analyzed data of 540 patients admitted within 24 h of stroke onset who were randomized to treatment with either paracetamol (6 g daily) or placebo. Blood pressures were measured at 12, 24, and 48 h from the start of treatment. Changes in blood pressure from baseline in the two treatment groups and corresponding 95% confidence intervals (CI) were calculated with linear regression analysis. Adjustments for potential confounders were made with a multiple linear regression model. Results - Treatment with high-dose paracetamol was associated with a significant reduction in systolic blood pressure of 4.5 mm Hg (95% CI 0.6-8.5) at 12 h from the start of treatment. This effect was no longer present after 24 and 48 h. Conclusion - High-dose paracetamol reduces not only body temperature but also systolic blood pressure in the first 12 h after start of treatment. Both effects may improve functional outcome after stroke, but this needs further study.