Background and Objectives: This study aimed to evaluate malnutrition prevalence and usefulness of the body mass index (BMI) in the assessment of malnutrition in hospitalized elderly patients with adrenal insufficiency (AI). Methods and Study Design: 318 hospitalized AI patients were diagnosed by a rapid ACTH stimulation test with a history of steroid treatment and compared with 374 control patients. Nutrition was assessed using the Malnutrition Universal Screening Tool (MUST). Nutritional status was evaluated using the Mini Nutritional As- sessment short form (MNA-SF) and BMI. Results: There was no difference in nutritional screening between the AI and control groups. Nutritional assessments indicated that 31.2% of all elderly patients suffered from malnu- trition and 33.8% of patients were at risk of malnutrition. Less than half of the patients (34.9%) were identified as well nourished. In this study, 33.6% vs 29.1% of patients were malnourished in the AI and control group, respec- tively. Overall, prevalence of malnutrition was higher in the AI group than the control group. In the AI group, pa- tients with low basal cortisol had a higher incidence of malnutrition than those with high basal cortisol. The BMI of patients in the AI group was higher than in the control group. According to BMI criteria, 64.3% of malnour- ished patients were overweight or obese in the AI group. Conclusions: Elderly AI patients are prone to develop malnutrition despite being overweight or obese. Therefore, more extensive nutritional assessment of elderly pa- tients with AI is required regardless of BMI.