Background/Objectives: This study aims to evaluate the prevalence and degree of malnutrition among patients with type 2 diabetes mellitus using the CONUT and PNI scores. Hypothesis: The CONUT and PNI scores provide a reliable assessment of the nutritional status of patients with type 2 diabetes. Methods: The retrospective study was run at the Department of Internal, Autoimmune and Metabolic Diseases in the Central Clinical Hospital of the Medical University of Silesia in Katowice from January to December of 2022. From 266 patients diagnosed with diabetes, only 64 met the criteria and were included in this study. Results: We found varying degrees of malnutrition among patients. Only 20.3% of them were well nourished. Mild to moderate malnutrition was observed in, altogether, 67.2% of patients. Conclusions: The strong correlation between the CONUT and PNI (r = −0.88) indices confirms their diagnostic value. The introduction of the CONUT or PNI tools into routine practice should be considered in patients with T2DM, especially those over 65 years of age, but taking into account the significant limitations of these indices and the influence of various factors on the laboratory data considered.