Genetic hemochromatosis (GH) is the most common autosomal-recessive disorder (1 in 300 in populations of Celtic origin). Homozygosity for a C282Y mutation in the hemochromatosis (HFE) gene is the underlying defect in approximately 80% of patients with GH, and 3. 2-13% of Caucasians are heterozygous for this gene alteration. Because the high frequency of this mutation may result from a selection advantage, the hypothesis was tested that the C282Y mutation confers protection against iron deficiency in young women. To address this question the genotype of codon 282 was determined in a cohort of 468 unrelated female healthcare workers, ages 18-40 years. In all study participants, a complete blood count was obtained, and erythrocyte distribution width, serum iron, transferrin, transferrin saturation, and ferritin were measured. Two individuals were homozygous for the C282Y mutation, 44 were heterozygous, and 416 were homozygous for the wild-type allele. Heterozygous women had significantly higher values for hemoglobin (P = 0.006), serum iron (P = 0.013), and transferrin saturation (P = 0. 006) than women homozygous for the wild-type allele. Our data provide evidence for a protective role of the C282Y mutation in the HFE gene against iron deficiency in young women and suggest that a more efficient utilization of nutritional iron may have contributed to the high prevalence of the mutation in Caucasian populations.