Malnutrition, considered for the purpose of the present data set as undernutrition, is a major risk factor of mortality in elderly people. Such protein-energy malnutrition should be detected as soon as possible. Once established, this malnutrition state must be corrected by appropriate diet, supplementation, artificial nutrition, or therapeutic treatment. If carried out well, these interventions should reduce the risk of mortality and, for some diseases such as degenerative diseases, may postpone morbidity and dependence. The efficiency of nutritional interventions has already been evaluated by different means including the measurement of anthropometric and laboratory parameters. However, in the absence of a consensus on the use of these parameters, comparison between studies and even effectiveness of the proposed treatment are frequently unconvincing. The relevance of the most common markers used in epidemiologic studies on malnutrition and nutritional interventions in elderly persons was studied for establishing a minimum data set. The aim of this task force was to provide investigators and operators in the field of clinical nutrition with clear and expert validated clinical outcomes allowing them to design and set up conclusive trials.