The benefits of herbal and other natural products (dietary supplements) are increasingly cited in the media. Dramatic increases in use reported during the last decade have led to growing concerns about efficacy and safety. US researchers determined which dietary supplements American adults use, whether or not the prevalence has continued to increase in recent years and whether or not the popularity of individual supplements has changed. Demographic information and details of use of all medicines and dietary supplements in the preceding week were obtained by telephone interview from February 1998 to December 2002 from households in 48 contiguous states and the District of Columbia. Participants included randomly selected residents of households with telephones; compared with 2000 US Census data, participants were representative of the US population. The main outcome measure was the weekly prevalence of dietary supplement use, alone or in a multicomponent product. There were 8470 subjects of 18 years or older. The annual prevalence of dietary supplement use increased from 14.2% in 1998–1999 to 18.8% in 2002. Although use did not change among younger subjects, it doubled for men and women 65 years or older. Use of Ginkgo biloba and Panax ginseng declined during the study, while lutein use increased dramatically because of its addition to multivitamin products. The overall 2002 prevalence excluding lutein use was 13.9%.