Stroke is one of the most devastating complications of patients with sickle cell disease (SCD). Currently, there are no known molecular or genetic markers that can be used to assess the risk of stroke in this population. We have previously shown that relative hypertension may be one risk factor for stroke in SCD. In a case-control study, we investigated the association between GT-repeat polymorphism within the angiotensinogen (AGT) gene and the risk of stroke in pediatric patients with SCD. After informed consent was obtained, 63 patients (21 stroke subjects and 42 nonstroke control subjects matched according to age and sex) with SCD followed at local pediatric hematology clinics were genotyped to test the association of specific GT-repeat alleles of the AGT gene and occurrence of stroke. There were statistical differences in the distribution of the genotypes among stroke and nonstroke SCD patients (chi(2) = 10.82, df = 11, P < 0.05). We also found GT-repeat alleles A3 and/or A4 of the AGT gene conferred a four-fold increase in the risk of stroke (odds ratio [OR] = 4, P < 0.05). The attributable odds ratio for allele A3 and A4 is 2.24 and 4.33, respectively (P < 0.005). Our results suggest that GT-repeat within the AGT gene may be associated with risk of stroke in pediatric SCD. The relative risk of stroke in the presence of alleles A3 and/or A4 is fourfold greater than in the absence of these alleles. If these data are substantiated in a larger cohort of patients, our results indicate that the determination of GT-repeat of AGT gene may be a useful genetic marker to assess the risk for stroke of patients with SCD. Am. J. Hematol. 68:164-169, 2001. Published 2001 Wiley-Liss, Inc.