Background: Folate and cobalamin are responsible for healthy growth. However, the B-vitamin and homocysteine status of adolescents is not well known. The aim was to assess the status of folate, cobalamin, and homocysteine in healthy Spanish adolescents. Methods: Serum cobalamin, serum folate, homocysteine, methylenetetrahydrofolate reductase 677C > T variant, BMI, smoking habits, and Tanner stage were determined according to gender in 165 adolescents (84 females, 81 males; 13-18.5 years) using the Student’s t test, Mann-Whitney U test and chi(2) test, respectively. Interactions between socioeconomic status, age group, methylenetetrahydrofolate reductase polymorphism, BMI, smoking habits, Tanner stage, and vitamin status, respectively, were examined by ANOVA or Kruskal-Wallis H test (p < 0.05). Results: Boys had markedly higher homocysteine (males 8.92 (5.51-22.94) mu mol/l; females 7.91 (5.09-13.86) mu mol/l), whereas girls showed higher serum cobalamin concentrations (males 540.00 (268.00-946.47) pmol/l; females 594.82 (280.63-1,559.64) pmol/l). Data are shown as medians and the 2.5th to 97.5th percentiles in parentheses. Adolescents with the homozygous variant of methylenetetrahydrofolate reductase displayed significantly higher homocysteine and lower serum folate: normal 5.73 (3.09-10.73) ng/ml serum folate, 7.57 (4.94-12.94) mu mol/l homocysteine; homozygous 4.10 (2.75-7.88) ng/ml serum folate, 10.83 (7.00-22.82) mu mol/l homocysteine. Conclusion: The present study provides data on the folate, cobalamin, and homocysteine status of Spanish adolescents. To assure a better assessment, revision of references for adolescents is still needed. Copyright (C) 2008 S. Karger AG, Basel.