We thank the authors for summarizing the Belgian experience with transcranial doppler (TCD) for children with sickle cell disease (SCD). Although their data are retrospective, they describe significant differences in the TCD velocities of children treated with hydroxyurea compared with those who were not. Similar to our findings, 1 children with highest baseline TCD velocities had the greatest treatment-related decreases. Their data also provide additional support for the use of hydroxyurea for primary and even secondary stroke prevention in children with SCD. We are encouraged that these pilot data further document the benefits of hydroxyurea for children with SCD, yet we maintain that treatment at the maximum tolerated dose is preferred. 2 As we concluded in our paper, controlled multicenter prospective trials are needed to determine the efficacy of hydroxyurea therapy in these clinical settings.