The use of iron supplements is an accepted treatment for nonhereditary anemia. The use of iron supplements as prophylaxis is more controversial. We estimated the proportion of persons who consumed supplements that contain iron among the following groups: nonpregnant, nonlactating adolescents, aged 14-18 y (n = 992); women aged 19-50 y (n = 5,062); women aged 51 y and older (n = 3,593); pregnant women (n = 295); and lactating women (n = 97) using data from the National Health and Nutrition Examination Survey, 1988-1994. We found that the proportion (% +/- SE) of U.S. women consuming supplements containing iron in the previous month was 9 +/- 2% among nonpregnant, nonlactating adolescents; 23 +/- 1% among women aged 19 y and older; 72 +/- 4% among pregnant women; and 60 +/- 8% among lactating women. Low income women were less likely to consume supplements containing iron. Minority women were less likely to consume supplements containing iron in all groups except adolescents. Among consumers of supplements that contain iron, the median intake of iron was 11 mg/d among nonpregnant adolescents, approximately 17 mg/d among nonpregnant women, 58 mg/d among pregnant women and 57 mg/d among lactating women. Use of supplements that contain iron was associated with a significantly reduced prevalence of iron deficiency among women 19-50 y but not among other groups. Groups at highest risk of iron deficiency (e.g., low income and minority women) are often least likely to consume supplements containing iron, suggesting that supplement use is unrelated to actual need.