Three hypotheses were tested: (1) clinically-silent cranial magnetic resonance imaging (MRI) abnormalities represented the minimal expression of the neurovascular diathesis, and were the harbingers of clinically-overt strokes (study A); (2) sickle cell disease patients who developed cerebral infarctions had a predisposing risk factor(s) that contributed to this neurological complication (study B); and (3) sickle cell disease patients developed a chronic encephalopathy and dementia that was independent of the neurovascular diathesis (study C). Study A was a prospective evaluation of 50 SCD children aged 6 to 12 years attempting to identify a subgroup of patients at risk for the development of a clinically-apparent stroke. These patients were evaluated clinically, and underwent MRI scan, magnetic resonance angiography (MRA), and single photon emission computerized tomography (SPECT). Study B represented two studies designed to analyze risk factors for stroke. The first study was a retrospective case-control analysis of 25 young adults who suffered one or more strokes. These patients were age-matched to an SCD control group which had been clinically free of strokes and had MRI, MRA, and SPECT studies. The second study represented a prospective case-control analysis of children who were being followed in study A. Study C represented a prospective study of 50 SCD children, and 50 age-matched siblings or closest available relatives. Annual neurological examinations and neuropsychological evaluations were performed searching for evidence of chronic encephalopathy and dementia. The longitudinal study design was necessary to dissect out the subtle variables that contributed to the cognitive deficits. The study was renewed in FY 1998 to continue through FY 2004.