Aims. To estimate the prevalence of use of nutritional supplements among young adults, to examine the source of those supplements and to investigate sex differences in usage. Methods. Participants in the age-26 years assessments of the Dunedin Multidisciplinary Health and Development Study were asked to bring containers for any medication (including supplements) taken in the previous two weeks. Medication data (including prescription source) were recorded and analysed for 978 of 980 Study members. Results. The prevalence of supplement use was 16.6%; 20.4% among females and 13.3% for males (p<0.01). Multivitamin preparations were the most widely consumed, followed by water-soluble vitamin supplements (such as folate and vitamin C). Folate use was higher among females and was taken by 35.7% of pregnant females. Most supplements were self-prescribed, although a doctor had prescribed over one-third of the mineral supplements. Most supplements had been taken for weeks or months, rather than years. Conclusions. Nutritional supplement usage among young adults is reasonably common, and involves a wide range of preparations. The extent of use among younger people suggests a need for regulation of their manufacture, sale and usage, and research to examine their efficacy.