The most common pathological change in eating behaviour among older persons is anorexia, which accounts for a large percent of undernutrition in older adults. The main research aims are to determine, in a sample of acute and rehabilitation elderly subjects, the prevalence of anorexia of aging and the causes most impacting on senile anorexia. METHODS: four different Units cooperated to this research study. Patients were recruited from geriatric acute and rehabilitation wards in Italy. Each Research Unit, for the estimation of the prevalence of anorexia in elderly subjects evaluated all the patients aged over 65 recruited from April 2006 to June 2007. Nutritional status, depression, social, functional and cognitive status, quality of life, health status, chewing, swallowing, sensorial functions were evaluated in anorexic patients and in a sample of "normal eating" elderly subjects. RESULTS: 96 anorexic subjects were selected in acute and rehabilitation wards (66 women; 81.5 +/- 7 years; 30 men: 81.8 +/- 8 years. The prevalence of anorexia in the sample was 33.3% in women and 26.7% in men. Anorexic subjects were older and more frequently needed help for shopping and cooking. A higher (although not statistically significant) level of comorbidity was present in anorexic subjects. These subjects reported constipation and epigastrium pain more frequently. Nutritional status parameters (MNA, anthropometry, blood parameters) were significantly worst in anorexic subjects whereas CRP was higher. Chewing and swallowing efficiencies were significantly impaired and eating patterns were different for anorexic subjects with a significant reduction of protein rich foods. CONCLUSIONS: consequences of anorexia can be extremely serious and deeply affect both patient's mobility, mortality and quality of life. Therefore, it is of utmost importance to perform a special evaluation of the nutritional risk, to constantly evaluate the nutritional status and feeding intake of older patients, to identify and treat the underlying disease when possible, to institute environmental and behavioural modifications, to organise staff better in order to produce higher quality feeding assistance during mealtimes, to plan early nutrition rehabilitation and nutritional education programs for caregivers. There is also the necessity to develop diagnostic procedures easy to perform, able to identify the pathogenesis of anorexia and, therefore, treatment strategies exactly fitting the patients' needs.