Abstract: To update its 1996 guidelines, the U.S. Preventive Services Task Force (USPSTF) commissioned this brief update of the evidence on selected questions about screening for iron deficiency anemia (IDA) in children, adolescents, and pregnant women. We searched relevant databases, Web sites, journals, and reference lists for systematic reviews, epidemiologic surveys, and controlled trials published in 1995 or later that contained new information about the prevalence, diagnosis, natural course, or treatment of iron deficiency anemia in asymptomatic persons in developed countries. One investigator rated the quality of included trials and summarized their results in tables. In the U.S., the average prevalence IDA in target groups is: Infants 1-2 years (6 to 17 per 1000), teenage girls (1.5%), nonpregnant females of reproductive age (2% to 5%). Factors associated with a higher prevalence include prematurity and low birth weight, black or Mexican-American race, Alaskan native heritage, recent immigration, poverty and, among teenage girls, fad dieting or obesity. The prevalence among pregnant women is not known. For cognitive and school outcomes, trials of iron supplementation for iron deficiency anemia have had mixed results. Most trials conducted in high-risk groups within developed countries did not demonstrate any benefit for infants and preschool children, but one trial in high-risk infants demonstrated a transient benefit.