Introduction: Detailed clinical information is important for the Casemix System to generate valuable Case Based Group (CBG) for malnourished geriatric patients. Clinical coding for malnutrition provides useful information on the nutritional health of patients for treatment purposes. Methods: This cross-sectional study with purposive sampling involved a total of 130 geriatric patients (>60 years) at Hospital Universiti Sains Malaysia (USM). Nutritional assessments were performed such as anthropometrics measurement, Subjective Global Assessment (SGA), and biochemical assessment. The patients’ medical records and coded data were systematically reviewed to observe the documentation of nutritional information and coding criteria based on the International Classification for Diseases (ICD-10). Results: The prevalence of malnutrition among the geriatric patients was 35.4%. Proper documentation of required nutritional information was found in less than 50% of the cases. None of the malnourished patients were documented and coded with malnutrition diagnosis, despite being given nutritional interventions. The reasons given for this omission were related to the lack of awareness (50%) and incomplete medical documentation (50%). Further analysis revealed that uncoded diagnosis, miscoding, missing, and unavailable codes for nutritional counselling and oral nutritional supplementation were the main contributors to the incomplete records. Conclusion: The quality of clinical coding for malnourished geriatric patients in the hospital should be improved. A structured assessment and standard documentation is recommended to improve the quality of healthcare provision for malnourished geriatric patients.