The risk of stroke during childhood in those with SCD is 1%/y, but patients with TCD evidence of high cere- bral blood flow velocities (time-averaged mean velocity >200 cm/s) have stroke rates >10%/y.551,552 Retrospective analysis of the Stroke Prevention Trial in Sickle Cell Anemia (STOP) data suggested that velocity >170 cm/s in the anterior cerebral artery is associated with increased stroke risk after controlling for the middle cerebral artery/internal carotid artery veloci- TCD surveillance of children with SCD remains the gold standard for stroke risk prediction, and its increased use coincides with a decrease in stroke among the pediatric SCD The optimal frequency of screening to detect patients at high risk has not been determined. The STOP study, which compared periodic blood transfusion with standard care in 130 children with SCD, used time-averaged means of the maximum velocity. Additionally, peak systolic velocity may be used, in which case a measurement of 250 cm/s is used as a threshold for prophylactic transfusion.556 In general, younger children and those with relatively high cerebral blood flow velocities should be monitored more frequently because of a higher risk of conversion to abnormal velocities in younger patients and in those with TCD velocities closer to 200 cm/s.557 Despite strong evidence of its value, overall TCD screening rates continue to be suboptimal as a result of patient and pro- The National Institutes of Health and the American Academy of Pediatrics recommend annual TCD screening from 2 to 16 years of age.560,561 Few studies have been done to determine whether TCD also predicts stroke in adults with SCD. 