Adequate protein intake and the maintenance of nitrogen equilibrium are of particular importance in the elderly because this age group is at increased risk of illness and malnutrition. The current recommendation for protein intake of healthy elderly subjects is 0.8 g/kg body weight/day, the same as for younger adults. Nitrogen balance studies in the elderly, however, revealed conflicting results; some studies suggest that not all elderly can achieve a nitrogen balance with a protein intake of 0.8 g/kg body weight/day, particularly if energy supply is not adequate. Beyond the amount of protein needed for nitrogen balance, the optimal protein intake for preservation of lean body mass, body functions, and health is of paramount interest. At present, there is insufficient longer-term research with defined health outcomes to derive recommendations in this regard. Very little is also known about the protein needs of frail and unhealthy elderly. Until more evidence is available, it seems reasonable to ensure a protein intake of at least 0.8 g/kg body weight/day in all elderly persons, particularly in those at risk of malnutrition (e.g., frail and multimorbid elderly). In addition to ascertaining adequate protein and energy intake, physical activity should be encouraged in order to increase energy expenditure and food intake and to facilitate muscle protein anabolism.