Abstract. Objectives: To determine the prevalence of thiamine deficiency in a high-risk group of elder emergency department (ED) patients who reside in nursing homes and need admission to the hospital, and to determine the effect of patients diets on this prevalence. Methods: This was an observational pilot study of 75 consecutive ED patients aged 65 years or older who lived in a nursing home and were admitted to the hospital. Plasma thiamine levels were measured by high-pressure liquid chromatography on serum samples collected within 24 hours of hospital admission. Nursing home records were reviewed to determine whether patients received nutritional supplementation or enteral tube feedings. Results: Seventy patients participated and had a mean plasma thiamine level of 27.3 μ/dL (95% CI = 20.2 to 34.4). Fourteen percent (n= 10, 95% CI = 8% to 24%) were thiamine-deficient (<10 μg/dL). Patients not receiving dietary supplements or tube feedings (n= 26) had lower mean thiamine levels (20.3 μg/dL, 95% CI = 12.7 to 27.9) and were thiamine-deficient more often (27%) than patients receiving dietary support (n= 44, 31.5 μg/dL, 95% CI = 24.7 to 38.3, 7% thiamine-deficient). Conclusions: Elder nursing home patients seen in the ED and admitted to the hospital are frequently thiamine-deficient. Empiric thiamine supplementation is often used in the ED for other high-risk patients, such as alcoholic individuals, and may be appropriate for high-risk elder patients. Further research is needed to determine whether thiamine supplementation in these patients can improve their clinical outcomes.