<i>Background/Aims:</i> A food frequency questionnaire (FFQ) and a database for dietary supplements were developed for use in the Norwegian Mother and Child Cohort Study (MoBa). The aim of the present study was to investigate the relation between reported use and biomarkers in supplement and nonsupplement users and to validate self-reported intake of dietary supplements in mid pregnancy. <i>Method:</i> 120 women were recruited from MoBa, and 119 subjects completed the MoBa FFQ and a 4-day weighed food diary. Information on supplement use was collected by both methods. Venous blood specimens and 24-hour urine samples were obtained for measurement of dietary biomarkers. <i>Results:</i> Biomarker concentration/excretion and intake differed significantly between supplement and nonsupplement users for vitamin D, carotenoids, folate, the n–6/n–3 fatty acid ratio and iodine (p < 0.05 for all variables). Flavonoid excretion was higher in flavonoid-supplement users (p < 0.05). Significant correlations between total dietary intake (food and supplements) and biomarker concentration/excretion were found for vitamin D (r = 0.45, p < 0.001), folate (r = 0.26, p = 0.005), the n–6/n–3 fatty acid ratio (r = 0.36, p < 0.001) and iodine (r = 0.42, p < 0.001). <i>Conclusion:</i> The biochemical indicators examined in this study confirmed differences in self-reported micronutrient intake between supplement and nonsupplement users for vitamin D, beta-carotene, folate, n–3 fatty acids, flavonoids and iodine.