Introduction: This study was conducted to evaluate the preoperative nutritional status of patients over 65 years of age, determine the factors affecting nutrition, and compare the effectiveness of the three screening tools that were used to evaluate nutritional status. Materials and Method: The research was cross-sectional and correlational. Two hundred elderly patients in the preoperative period of the surgical service were interviewed. The Mini Nutritional Assessment short form (MNA-SF), Nutritional Risk Screening form (NRS-2002), and Geriatric Nutritional Risk Index (GNRI) were used. Results: Elderly patients—35.0% according to the MNA-SF, 35% according to NRS-2002, and 39.5% according to GNRI —were found to have a higher risk of preoperative malnutrition. A significant correlation was found between dysphagia and loss of appetite in elderly patients and the risks of malnutrition. Based on Receiver operating characteristic analysis, GNRI and MNA-SF were found to have high diagnostic value for preoperatively diagnosing malnutrition in elderly patients (area under the curve 0.95 and 0.90, respectively). The highest sensitivity (93.7%) belongs to Geriatric Nutritional Risk Index. Conclusion: The use of the Geriatric Nutritional Risk Index tool is appropriate in evaluating the preoperative nutritional status in elderly patients.