A hypothetical cohort of 1000 children with SCA and strokes followed for 5 years receiving either no therapy, hydroxyurea therapy, or regular blood transfusion therapy. Stroke recurrence in the no-treatment group, hydroxyurea therapy group, and regular blood transfusion therapy group have expected incidence rates of 29.1 (95% CI, 19.2-38.9), 3.8 (95% CI, 1.9-5.7), and 1.9 (95% CI, 1.0-2.9) events per 100 patient-years.