Methods: Inclusion criteria include consecutive adult patients with acute ischemic stroke within 12 hours of onset admitted to participating centers. A cluster (month) method of randomization to lying flat or upright head position for 48 hours, stratified by site The primary outcome is change in mean CBFV measured by TCD at 24 hours. Secondary outcomes include proportion of adverse events at 7 days, distribution of NIHSS at 7 days, and distribution of mRS disability scale scores at 90 days. Sample size is 46 clusters of 2 patients totaling approximately 92 patients to detect an increase of 8.31 (CI 95% 4.82-12.0) cm/sec in average CBFV from 30° to 0° head position. This sample size will also allow detection of that difference with 90% power at a 5% significance level, considering an ICC of 0.037.