BACKGROUND: The use of dietary supplements (DS) has steadily increased over the last several decades, particularly among older adults, contributing to the growth of the multibillion-dollar DS industry. The cost of prescription medication is a known contributor to medication nonadherence, yet the cost burden of DS among older adults is not well understood. METHODS: Using medication data from the 5-year multicenter longitudinal cohort AAA LongROAD study of older adults who drive, DS were identified and categorized. Cost estimates were based on prices obtained from a popular online marketplace, using dosing and frequency recommendations from the National Institutes of Health Office of Dietary Supplements database. ANOVA was used to explore associations between demographics and DS cost burden. RESULTS: Of the 2,990 participants at baseline, 2068 (69%) followed up through year 5. The number of DS users ranged from 70.4 to 82.7% of the participants from baseline to year 5. Among the 160 supplement formulations identified, 142 (88%) had price data and were included in the analysis. The mean estimated cost of individual supplements ranged from .73 to 9.59 per month. The mean monthly cost burden for all older adult participants ranged from 0.23 (SD 14.74) at baseline to 3.14 (SD 16.93) in year 3, with a mean annual cost burden of 42 per participant across all years. The mean monthly cost burden for DS users only ranged from 4.56 (SD 15.59) at baseline, to 6.45 (SD 17.45) in year 3, with a mean annual cost burden of 86 per DS user across all years. Increased spending was associated with female gender, older age, higher income, not working, and being White non-Hispanic. CONCLUSION: The use of DS is common among older adults. Using conservative estimates of monthly cost, the spending of older adults on DS is high. The real-world impact of DS costs on older adults, such as the impact on the affordability of prescription medication, is a key point for future research. CLINICAL TRIAL NUMBER: Not applicable. TRIAL REGISTRATION: Not applicable.