Micronutrient inadequacies are common in older adults and using a multivitamin/multimineral supplement (MVM) may improve their nutritional status. National Health and Nutrition Examination Survey data were analyzed to determine micronutrient intakes based on diet and MVM use in adults aged ≥51 years. Deficiencies were evaluated using nutrient biomarkers. The National Cancer Institute Method was used to estimate usual intakes of 18 micronutrients stratified by age and frequency of MVM use. Compared with food alone, MVM use was associated with higher nutrient intake and lower prevalence of inadequacies of almost all micronutrients examined and improved nutrient biomarker status of folate, iodine, selenium, and vitamins B, B, and D. Regular MVM use (≥16 days/month) decreased the odds of clinical deficiency (defined by biomarker status) of vitamins B and D but increased the proportion exceeding the tolerable upper intake level of folic acid. Vitamin B deficiency in MVM non-users was common and increased with age.