BACKGROUND: Iron deficiency anemia (IDA) frequently occurs in adolescents because of accelerated physical growth in boys and girls. This was aimed at assessing the prevalence of iron deficiency and IDA in apparently healthy Korean adolescents according to the gender and age. METHODS: Apparently healthy students(M: F=1: 1.2) aged 11 to 24 years were included in this study and blood samples were obtained from April to May, 2000. Hemoglobin, hematocrit, red blood cell indices, serum ferritin, iron and total iron-binding capacity were measured. RESULTS: In males, the prevalence of iron deficiency was 15.7% in the 11~12 years group, 16.1% in the 13~14 years group, 9.9% in the 15~16 years group, and 6.4% in the 17~18 years group. In females, the prevalence of iron deficiency was 26.8% in 11~12 years group, 27.9% in the 13~14 years group, 38.8% in the 15~16 years group, 36.0% in the 17~18 years group, 30.9% in the 19~24 years group. The prevalence of IDA in males was 3.6% in 11~12 years, 2.1% in 13~14 years group, 1.9% in 15~16 years group, and 0.6% in 17~18 years group. The prevalence of IDA in females was 4.2% in 11~12 years, 9.7% 13~14 years, 20.4% in 15~16 years, 16.2% in 17~18 years group, and 12.4% in 19~24 years group. CONCLUSION: As the prevalence of iron deficiency and IDA were substantially greater than expected, studies of iron state in adolescent girls, especially middle to high school age, should be undertaken to assess iron deficiency.