To characterize supplement use within a sample population of men diagnosed with prostate cancer. A census of men diagnosed with prostate cancer at Duke University Medical Center from 1997 to 2002 (n = 1402) was mailed a survey that ascertained data on health status, education, diet, exercise, smoking status, and information on supplement use. Differences between demographic and treatment subgroups were described and tested, as was change in supplement use after diagnosis. Data from 805 respondents indicated that a majority (73%) used supplements, and 68% claimed that this information was shared with their cancer care provider. The most commonly reported supplements were multivitamins (56%), vitamin E (43%), vitamin C (33%), and calcium (26%). On average, 2.7 +/- 2.8 supplements per day were taken, and use increased significantly after diagnosis for most supplements. Use was significantly higher among men who were white (P = 0.043), were more highly educated (P = 0.002), exercise regularly (P = 0.020), and who consume five or more daily servings of fruits and vegetables (P = 0.040). A high percentage of men with prostate cancer take supplements, especially those who are white, more educated, and who pursue healthful behaviors. Systematic means of capturing these data are necessary to begin to understand the potential impact of supplements on disease outcome, especially because no data exist to suggest that supplements are of any benefit after diagnosis.