About 20%-50% of patients in hospitals are undernourished. The number varies depending on the screening tool amended and clinical setting. A large number of these patients are undernourished when admitted to the hospital, and in most of these patients, undernutrition develops further during hospital stay. The nutrition course of the patient starts by nutritional screening and is linked to the prescription of a nutrition plan and monitoring. The purpose of nutritional screening is to predict the probability of a better or worse outcome due to nutritional factors and whether nutritional treatment is likely to influence this. Most screening tools address four basic questions: recent weight loss, recent food intake, current body mass index, and disease severity. Some screening tools, moreover, include other measurements for predicting the risk of malnutrition. The usefulness of screening methods recommended is based on the aspects of predictive validity, content validity, reliability, and practicability. Various tools are recommended depending on the setting, ie, in the community, in the hospital, and among elderly in institutions. The Nutrition Risk Screening (NRS) 2002 seems to be the best validated screening tool, in terms of predictive validity ie, the clinical outcome improves when patients identified to be at risk are treated. For adult patients in hospital, thus, the NRS 2002 is recommended.