OBJECTIVES: To analyze baseline data on concomitant use of prescription drugs and dietary supplements in elderly people from the Ginkgo Evaluation of Memory (GEM) Study, in which information was collected on all drugs and supplements used by participant. DESIGN: Cross-sectional correlation analysis. SETTING: GEM Study sites in California, Maryland, North Carolina, and Pennsylvania. PARTICIPANTS: Three thousand seventy ambulatory individuals aged 75 and older enrolled between September 2000 and June 2002. MEASUREMENTS: Use of prescription drugs and dietary supplements identified through bottles brought to the clinic. RESULTS: Almost three-quarters (74.2%) of the cohort combined use of at least one prescription drug and one dietary supplement, with 32.5% using three or more prescription drugs and three or more supplements. The 15 most-prevalent prescription drugs exhibited substantial concomitant use with dietary supplements, ranging from 77.6% for diuretics to 93.6% for estrogen preparations. Although supplements were taken concomitantly with all classes of prescription drugs, the use of supplements was more likely in individuals using nonsteroidal anti-inflammatory drugs, thyroid drugs, and estrogens. The use of drugs for diabetes mellitus was negatively associated with the use of supplements, with most of this attributed to low use in those taking multivitamins, glucosamine and chondroitin, and echinacea. CONCLUSION: There is substantial concomitant use of prescription drugs and dietary supplements in elderly people. Further investigations are needed to define the clinical importance of this concomitant use, especially in elderly patients who consume multiple prescription drugs or have experienced an adverse event secondary to their prescription medications.