The link between beta s-gene haplotypes and sickle cell anemia has permitted a better understanding of the biological manifestations of this disease. The use of better laboratory methods can help rule out other hereditary factors that can camouflage the real hemoglobin genotype. The clinical heterogeneity of sickle cell disease, which is characterized by the presence of S hemoglobin, can be explained in terms of fetal hemoglobin (HbF) levels, ratio of G gamma chains to A gamma chains, 2,3-diphosphoglycerate levels, linked mutations, beta s haplotypes, coexistence of alpha-thalassemia, and environmental factors. The inheritance of Sen and Arab/Indian beta-gene cluster polymorphisms is associated with a milder clinical course, whereas the Central African Republic (CAR) or Bantu, Cameroon, and Benin haplotypes are linked with severe sickle cell disease. The CAR haplotype carries the worst prognosis of all (less than 12% HbF levels and adult-type G gamma:A gamma ratio). Once characterized, these DNA polymorphisms also assume great importance as anthropologic and genetic markers. In America, beta s haplotypes are contributing to a better understanding of Black American roots and their African ancestry. There is ample evidence of genetic variability not only between different Black populations in America, but also within the same country, as is the case in Costa Rica.