Development of a simple, validated Nutrition Risk Score for identification of patients at risk of undernutrition is described. The score is easy to use, applicable to all patient categories and ages, and correlated well with a validated Nutrition Risk Index (r = 0.68, p < 0.001) and clinical impression (r = 0.83, p < 0.001). Reproducible scores were obtained between dietitians (r = 0.91, p < 0.001) and between dietitians and nursing staff (r = 0.80, p < 0.001). The score was used to assess risk of undernutrition in 153 consecutive admissions to medical and surgical specialties. Patients were categorised as low (50%), moderate (24%) or high risk (26%). Evaluation of measures to prevent nutritional depletion revealed that no action was taken in 64% (23/36) of moderate risk and 30% (12/40) of high risk patients. Implementation of routine, hospital-wide nutritional screening, to identify patients in need of nutritional support, has been achieved by inclusion of the score in the standard nursing assessment process.