Although the Stroke Prevention Trial in Sickle Cell Anemia (STOP) demonstrated the efficacy of blood transfusions for primary stroke prevention in high-risk children with sickle cell disease (SCD) in 1998, the impact of this trial on public health has not been studied. Our objective was to determine whether stroke rates in Californian children with SCD have declined since 1998. Using a California-wide hospital discharge database, we identified all first admissions for stroke in children with SCD from 1991 through 2000. Annual stroke incidence rates were calculated as the number of admissions divided by the estimated population of Californian children with SCD in that year. For 1991-2000, 93 children with SCD were admitted to Californian hospitals with a first stroke during 12 030 person-years of follow-up; 92.5% were ischemic and 7.5% hemorrhagic. Overall, the rate of first stroke was 0.77/100 person-years. For the study years 1991-1998, the rate for first stroke was 0.88/100 person-years compared to 0.50 in 1999 and 0.17 in 2000 (P <.005 for trend). Since the publication of the STOP study in 1998, annual rates of admissions for first stroke for Californian children with SCD have declined.