Sample size: We plan to recruit about 2000 patients. The Trial will have > 90% power (alpha 0.05) to identify an absolute reduction of risk of our primary outcome of 4% (10% to 6%). The frequency of our primary outcome is estimated from the ongoing CLOTS Trials 1 & 2 which use the same entry criteria and methods of follow up. The estimated effect size (odds reduction = 43%) is based on the treatment effects in the systematic review of previous stroke trials (odds reduction = 48%) attenuated by the delays in applying the treatment due to trial recruitment and realistic estimates of adherence to the allocated treatment. If the event rate in both treatment groups combined is lower than expected the Trial Steering Committee may decide to increase the recruitment target. We aim to enrol at least 1500 patient on Days 0−2 after stroke onset. This will provide greater than 80% power to detect a reduction in proximal DVT from 10% to 6% in patients enrolled on Days 0−2. If the proportion enrolled after Day 2 exceeds 25% of the total then the Trial Steering Committee will consider raising the overall target beyond 2000 to ensure that at least 1500 are recruited on Days 0−2. This should help ensure that we do not miss a real treatment effect because of delays in recruitment. If the trial shows that IPC is effective in reducing the risk of DVT after stroke it is likely that IPC treatment will be started earlier than in the trial.