Dietary supplement use is increasingly common in the United States. Multivitamin formulations with or without minerals are typically the most common type of dietary supplement reported in surveys and studies that collect data relating to dietary supplement use. In the National Health and Nutrition Examination Survey (NHANES) 1999-2000, 52% of adults reported taking a dietary supplement in the past month, and 35% reported regular use of a multivitamin-multimineral (MVMM) product. NHANES III data indicate an overall prevalence of dietary supplement usage of 40%, with prevalence rates of 35% in NHANES II and 23% in NHANES I. Women (versus men), older age groups, non-Hispanic whites (versus non-Hispanic blacks or Mexican Americans), and those with a higher education level, lower body mass index, higher physical activity level, and more frequent consumption of wine had a greater likelihood of reporting use of MVMM supplements in NHANES 1999-2000. Data from children suggest a similar prevalence rate, but lower prevalence rates of usage were reported in studies of adolescents. Individuals who use dietary supplements (including MVMM formulations) generally report higher dietary nutrient intakes and healthier diets in studies in which dietary data were also collected. Among adults with a history of breast or prostate cancer, usage rates for dietary supplements in general and MVMMs are considerably higher (eg, 56-57% for MVMMs), and these subgroups are more likely to also report use of single vitamin and mineral supplements. Thus, MVMM use contributes a considerable proportion of nutrient intakes in the United States and may contribute to risk of excessive intakes.