We estimated the prevalence of postpartum iron deficiency, anemia and iron deficiency anemia in the United States and compared risk of iron deficiency between women 0-24 mo postpartum (n = 680) and never-pregnant women, 20-40 y old (n = 587). We used data from National Health and Nutrition Examination Survey, 1988-1994. Iron deficiency was defined as abnormal values for > or = 2 of 3 iron status measures (serum ferritin, free erythrocyte protoporphyrin, transferrin saturation). Iron deficiency prevalences for women 0-6, 7-12 and 13-24 mo postpartum were 12.7, 12.4 and 7.8%, respectively, and 6.5% among never-pregnant women. After adjustment for confounding, the risk of iron deficiency among women with a poverty index ratio < or = 130% who were 0-6, 7-12 and 13-24 mo postpartum was 4.1 (95% confidence interval 2.0, 7.2), 3.1 (1.3, 6.5) and 2.0 (0.8, 4.1) times as great, respectively, as never-pregnant women with a poverty index ratio > 130%, but risk was not elevated for never-pregnant women with a poverty index ratio < or = 130%. Compared with the same referent, the risk of iron deficiency was not meaningfully different for women with a poverty index ratio > 130% who were 0-6, 7-12 or 13-24 mo postpartum. Given that low income postpartum women bear a substantially greater iron deficiency risk than never-pregnant women, more attention should be given to preventing iron deficiency among low income women during and after pregnancy.