We have evaluated the hypothesis of a negative association between glucose 6-phosphate dehydrogenase (G6PD) deficiency and cancer in a cohort of 481 Sardinian males with hematological malignancies. The frequency of G6PD deficiency in the patients was not different from the incidence in a group of 16,219 controls. The same conclusion resulted from the comparison of the frequency of expression of the GdB gene in 23 heterozygous women having a clonal hematologic disease and a control group of 37 healthy heterozygotes. Therefore at present there is no evidence that G6PD deficiency has a protective effect against development of hematologic neoplasms.