The prevalence of glucose-6-phosphate dehydrogenase (G6PD) deficiency and sickle cell trait was determined in 371 Cameroonian males and 668 male blood donors in Chicago. The number of males with both sickle cell trait and G6PD deficiency was significantly greater than expected (p < 0.05) in Cameroon. The number of males with both sickle cell trait and G6PD deficiency in the Chicago population also exceeded the expected number, although this was not statistically significant (p > 0.30). A young red cell population associated with the sickle cell gene leading to elevated G6PD levels in G6PD-deficient males suggests that sickle hemoglobin may exert a beneficial effect on G6PD deficiency, rather than the opposite, as had previously been proposed. These red cells may be better able to deal with oxidative stress, which can precipitate severe hemolytic disease in G6PD deficiency.