(Commentary on Hijmans et al., page 783) T he article by Hijmans et al. [1] in the current issue of Pediatric Blood and Cancer, notes that the ''most devastating complication of sickle-cell disease (SCD) is cerebral vascular infarction.'' Although stroke in SCD has been recognized for 80 years, the past three decades have seen an increasing number of reports describing the neuropsychological performance of children with SCD [2][3][4]. Over the same period, an improved, but still incomplete, understanding of the pathophysiology of SCD in the brain has been gained [5]. The association of stenosis or occlusion of large intracranial arteries and stroke was first demonstrated by cerebral angiography. Subsequently, transcranial Doppler ultrasonography (TCD) screening has allowed identification of those with abnormally elevated cerebral artery flow velocities who are at very high risk for stroke and the dramatic reduction in the incidence of stroke through transfusion management [6]. Both overt strokes and cerebral silent infarcts on MRI of the brain are associated with cognitive deficits and diminished school performance [7]. Abnormalities in cerebral blood flow may be a common pathophysiologic factor for CNS injury [8], but our understanding of the incidence, pathophysiology, prognosis, and appropriate treatment of diminished neurocognitive performance remains limited.In the Hijmans study, 41 subjects, ages 6-18 years, with HbSS or HbSb 0 -thalassemia were evaluated with a well-defined battery of tests to measure general intelligence (full-scale IQ), executive function, and visuo-motor function. Subjects were seen at a center in the Netherlands and were mostly low socio-economic status (SES) immigrants from western African and Surinam. Importantly, the investigators evaluated an ethnicly and SES-matched control group of healthy siblings of the tested cohort or of other patients with SCD who were receiving care at the same hospital. Among the subjects with SCD were 3 who had had an overt stroke and 6 who were receiving chronic transfusion. Major findings were that SCD was associated with markedly lower IQ scores (one-third had FSIQ <75), diminished visuo-motor function, and executive dysfunction, including deficits in sustained attention, planning, and visuo-spatial working memory.The study had several important strengths. First, SCD subjects were compared to a control group, unlike many investigations which have lacked appropriate controls. Secondly, the subjects represented a different and perhaps more globally heterogeneous group than the African-American population which typically has been examined. Thirdly, the neuropsychometric instruments utilized in the study were well defined and specifically targeted at executive and visuo-motor function, domains known to be particularly compromised in SCD [2,3].The study also had significant limitations. First, it was unclear how the three patients who had experienced overt strokes influenced the overall results, since individual patient data was not included. It is poss...