Participants of the Multiethnic Cohort Study in Hawaii and Los Angeles, California, a representative sample of African-American, Native Hawaiian, Latino, Japanese-American, and White adults, completed a baseline questionnaire in 1993-1996 assessing dietary supplement use during the past year as well as demographic, dietary, and other lifestyle factors. Factors associated with supplement use were examined among those who reported an absence of chronic disease (n = 100,196). Use of any of eight supplements at least once per week during the past year ranged from 44% among Hawaiian men to 75% among Japanese-American and White women. Multivitamins were the most frequently reported supplement; 48% of the men and 56% of the women reported regular use. Dietary supplement use was high across all ethnic groups, although levels and length of regular use varied. In all gender-specific ethnic groups, supplement use tended to increase with age, education, physical activity, fruit intake, and dietary fiber intake and to decrease with obesity, smoking, and dietary fat intake. Participants whose lifestyles were healthier were more likely to use dietary supplements. Therefore, it may be difficult to separate the effects of supplement use from other lifestyle factors when studying disease etiology.